It is with great sadness I must admit that "snuck" is a word. My proofreading software doesn't think it is, because I'm staring at a red squiggle under that word, but alas, it has found its way into dictionaries. The general consensus now is that both words are interchangeable, and the grammar world as a whole has reluctantly embraced this new word.
Some people claim that "snuck" is transitive--it needs another word to dump its action onto--while "sneaked" is intransitive--the sentence could stop with it (although it usually has prepositional phrases dangling after).
I snuck food onto the plane.
Much to my chagrin, this word has sneaked into dictionaries.
I know I used one as a simple past and the other as past participle, but that is beside the point. Both words can be used as both types of past. Or so they say.
I for one will never be caught using this word, for in the creative description of a random grammarist.com commenter, "‘Snuck’ sounds like an onomatopoeia for someone sucking snot back up his nose."