The Sugar Bowl, also known as the Vessel For Disaccharides, is a mysterious object mentioned repeatedly in A Series of Unfortunate Events. It has never explained what is inside of it.
The Sugar Bowl is important to V.F.D. and it has been stolen. There are many mentions of the sugar bowl and both sides of V.F.D. seem to be pursuing it; the Baudelaire orphans are eventually caught up in the search, although they have no idea why the bowl is so important.
It was first mentioned by name in The Hostile Hospital, in which Lemony Snicket (as the narrator) ponders whether it was necessary to have stolen it from Esmé Squalor. It is mentioned in The Ersatz Elevator and The Hostile Hospital by Esmé. Lemony Snicket and Beatrice Baudelaire seem to have been in part to steal it. It is implied that the sugar bowl is currently in possession of Lemony after he retrieved it from the pond next to Hotel Denouement.
In Lemony Snicket: The Unauthorized Autobiography, it becomes apparent that it contains an object of great power or danger.
Lemony Snicket's narration has been pivotal in exploring the sugar bowl's relevance to the overall plot. Where the sugar bowl came from and when an item of importance was hidden in it are unclear; however, it is generally agreed that the earliest point in its significant history is referred to in The Grim Grotto and The Slippery Slope. In the former, Esmé Squalor claims that Beatrice stole the sugar bowl from her, but in the latter, Lemony Snicket claims that he stole the sugar bowl from Esmé. Clues in these books indicate that Beatrice was at a tea party held by Esmé when the sugar bowl was taken from her, and Esmé may have then mistakenly deduced that Beatrice was the thief. Esmé's house on 667 Dark Avenue had a secret passageway connected to the Baudelaire Mansion, so it is plausible that Esmé used it to burn down the property as a vendetta against Beatrice. It is also possible that Beatrice and Lemony worked together to steal the bowl. This may be the crime that Lemony Snicket and Beatrice committed together before her death, as mentioned in 13 Shocking Secrets You'll Wish You Never Knew About Lemony Snicket. However, this crime is more likely to be the murder of Count Olaf's parents.
In The Slippery Slope, Lemony Snicket mentions in a letter to his sister that her "suggestion...that a tea set would be a handy place to hide anything important and small...has turned out to be correct." A sugar bowl is one of the parts of a tea set. Later in the book, Violet Baudelaire notes that a tea set used by Count Olaf and Esmé Squalor is missing an item, implied to be a sugar bowl when Violet later fibs that she and her siblings know the sugar bowl's whereabouts. The High Court judges (Count Olaf's bosses) searched the destroyed V.F.D. office after the fire they set to find the sugar bowl, but did not find it, the bowl having been thrown out the window before the fire.
It is also mentioned in The Dismal Dinner that a sugar bowl was passed around at the Baudelaire parents' fourth-to-last dinner party, but it is unclear whether this is the same sugar bowl that was stolen from Esmé.
In The Unauthorized Autobiography, a letter to Lemony Snicket from the Vineyard of Fragrant Drapes (likely a V.F.D. related place, because of its initials and the use of the Sebald Code in the note) mentions that "all the sugar bowls will be in place". Later, a similar letter can be found to Jerome Squalor about his marriage to Esmé, although that letter is from the Vineyard of Fragrant Grapes. The latter letter also states "that they were unable to provide the sugar bowls your fiance requested in a separate letter," hinting again that the Vineyard is part of the fire fighting side of V.F.D.
At some point, the sugar bowl was taken to the V.F.D. headquarters in the Mortmain Mountains. At a point prior to The Slippery Slope, the man with a beard but no hair and the woman with hair but no beard burnt down the headquarters but were unable to recover the sugar bowl; Lemony Snicket states in the narration that a brave volunteer threw the bowl out the window into the Stricken Stream, knowing it would be swept away and be saved from the villains.
In The Grim Grotto, Klaus Baudelaire and Captain Widdershins believed it to have washed into the Gorgonian Grotto, but when the grotto was explored, the bowl was not there; the narration implies that the bowl had been removed quite some time before. It is here that the Baudelaires are told that the sugar bowl itself is not important; it's the contents of the bowl that matters.
In The Penultimate Peril, the sugar bowl was brought to the Hotel Denouement by V.F.D. crows. The plan, on the villains' part, was to capture it by harpooning the crows, but due to the actions of Dewey Denouement, a plan was put in place to prevent the villains from securing it. The volunteers and villains originally thought it had fallen into the laundry room, but the Baudelaires later conclude that the sugar bowl had fallen into the pond. However, in a twist, Snicket implies that the bowl was retrieved from the pond and carried away by taxi shortly before the destruction of the hotel, and that this taxi driver was possibly himself, implying that Lemony currently has the sugar bowl. However, in this book, a major clue about the contents of the sugar bowl is written. As Esmé said, the sugar bowl holds 'it' "safely, securely, and attractively." Also, many people have lost their lives searching for the sugar bowl, and 'it' is extremely important to the Baudelaires and the Snickets.
In The End, there is a possible mention of the sugar bowl. When reading an extract from A Series of Unfortunate Events (the history of the island at which the Baudelaires arrive), Klaus reads, "Beatrice is hiding a small amount [of horseradish (or other substance capable of diluting the medusoid mycelium)] in a vess-". It could be assumed that the sentence would continue as "a vessel for disaccharides." Whether this is a reference to the same sugar bowl that was stolen from Esmé Squalor, or simply that sugar bowls became common in V.F.D. as they proved useful for storage of sensitive items, is not known.
Lemony Snicket: The Unauthorized Autobiography's index entry for the sugar bowl redirects the reader to the entries for 'hiding places' and Lena Pukalie's book I Lost Something at the Movies, a reference to real-life film critic Pauline Kael's I Lost It at the Movies; the link between the latter and the sugar bowl is not explained. However, Pauline Kael has said the word 'it' refers to "so many kinds of innocence" -- Lemony could be referring to an item that proves or embodies innocence.
Hints and theories about contents
There are many clues and hints about the sugar bowl and what it is, but Lemony Snicket does not reveal its secret at all in the series, leaving an element of suspense for the readers.
- The Slippery Slope indicates that the sugar bowl contains something that proves Lemony Snicket innocent of arsons committed by Count Olaf; The Penultimate Peril implies that Lemony Snicket has gained possession of the bowl. If this is the case, Snicket may have gone on to use the sugar bowl to clear his name; The Beatrice Letters reinforces this, as by the time its later segments take place, Snicket is apparently able to publicly rent an office and have mail delivered there, something he would be unable to do as a wanted fugitive.
- Esmé Squalor, when confronting the Baudelaires, Dewey Denouement, and their associates in The Penultimate Peril, emphasized the difficulty of finding a container that could hold the sugar bowl's contents safely, securely, and attractively, and stated many lives were lost in the quest to find it; she also states that it means very much to the Baudelaires and the Snickets. However, it is unclear where she is referring to the sugar bowl and where to its contents.
- There is also another possible use for the sugar bowl: it could contain the figurine mentioned in The Carnivorous Carnival, since it was said to contain "vital evidence" and was relatively small.  If this theory is true, then the figurine was probably placed inside the sugar bowl as it winded down the Stricken Stream and possibly taken away, which would be the reason that the Baudelaires didn't find it in the Gorgonian Grotto.
- The sugar bowl could also contain something of great power, perhaps even greater than the Medusoid Mycelium. This is because Dewey says that Count Olaf wouldn't dare use the Mycelium if he (Dewey) has the sugar bowl. This might imply that Dewey could use the contents to retaliate, either because it contains some sort of weapon or if it contains evidence that could be used to convict Olaf of a crime, prove Lemony Snicket's innocence or both.
- The Sugar Bowl also may contain horseradish, the only cure to the Medusoid Mycelium (except for wasabi, which is a culinary equivalent). Proof of this is in The End, where in the commonplace book "A Series of Unfortunate Events" where it says
|“||Ishmael's fear mongering has stopped work on the passageway, even though we have a plethora of horseradish in case of any emergency. We're attempting a botanical hybrid through the tuberous canopy, which should bring safely to fruition despite its dangers to our associates in utero. Of course, in case we are banished, Beatrice is hiding a small amount in a vess--||”|
- The "vess" part can be assumed to be Vessel For Disaccharides. 
- One theory is that the sugar bowl is merely a MacGuffin, a plot device whose contents of it are actually completely irrelevant and whose function is simply to be a much sought-after object that motivates characters and drives the story along.
- One theory is that the sugar bowl is empty, and its contents fell out a long time ago.
- One theory is that the sugar bowl simply contains sugar.
- One theory is that there is a microphone in the sugar bowl, recording secrets.
- One theory is that the Sugar Bowl contains the Bombinating Beast statue from All the Wrong Questions.
- Some believe that there are actually multiple Sugar Bowls
The sugar bowl appears in the TV series.
It is first foreshadowed in "The Bad Beginning: Part Two" when Count Olaf says he can not find it.
- Daniel Handler comments, "The mystery of the Sugar Bowl is clear enough that one that about reader a year writes me and has figured it out, and that fills me with pleasure. That makes me think it's not too obscure. If no one ever wrote me about it I would think, "Oh I didn't do it enough." But because one person a year who will write me and say, "I figured it out." The whole answer of the Sugar Bowl is solvable."
- There is a VFD quote saying, Tea should be as bitter as wormwood, and as sharp as a two-edged sword."