1: If the group that the narrator meets is assumed not to be travelling to St. Ives (this is the most common assumption), the answer would be one person going to St. Ives; the narrator.
2802: If the narrator met the group as they were also travelling to St. Ives (and were overtaken by the narrator, plausible given the large size of the party), the answer in this case is all are going to St. Ives; see below for the mathematical answer.
2800: If the narrator and the group were all travelling to St. Ives, the answer could also be all except the narrator and the man since the question is ambiguous about whether it is asking for the total number of entities travelling or just the number of kits, cats, sacks and wives. This would give an answer of 2800 — 2 fewer than the answer above.
2: Two is also a plausible answer. This would involve the narrator meeting the man who is assumed to be travelling to St. Ives also, but plays on a grammatical uncertainty, since the riddle states only that the man has seven wives (and so forth), but does not explicitly mention whether the man is actually accompanied by his wives, sacks, cats, and kittens.
0: Yet another plausible is zero, once again playing on a grammatical uncertainty. The last line of the riddle states “kits, cats, sacks, wives … were going to St. Ives?” Although the narrator clearly states he is going to St. Ives, by definition he is not one of the kits, cats, sacks, or wives, and based on the common assumption that the party was not going to St. Ives, the answer is zero.
2753: The sacks are not a person or animal and therefore cannot be in the calculation. It was not the number of things, but of “persons” the narrator met. 49 adult cats 343 kittens per wife of whom he had seven (7 × 392) = 2744 plus the seven wives 2751 plus the man the narrator → 2753 persons and animals.
9: There are nine people involved, who may be going to St. Ives. The animals are all in the sacks, so they, as well as the sacks themselves, are “being taken”, rather than “going”.
7: There are nine people involved, who are the only ones who may be going to St. Ives, all the others “being taken” there. But since the question is limited to “Kits, cats, sacks, wives”, this excludes the man and the narrator, leaving seven.