Snuck is used in American and Canadian English as the past tense and past participle of sneak, but it is considered non-standard, i.e., ol for dialectal and informal speech and writing. The standard past tense is sneaked. Snuck is relatively new, an Americanism introduced in the late 19th century. The opposite has occurred to the past form of slink. Slunk was long the standard form, but then slinked appeared and is encroaching on slunk. Slinked is considered non-standard. Style guides at some of the biggest newspapers in Canada and the United States - including the Globe and Mail (1998) and the New York Times (1999) - ban snuck. But snuck may tiptoe into more formal writing over the years.
On the way to the in-laws a couple weekends ago, I was in the rightmost lane on the 401 and it occurred to me that there were a whole lot of lanes to my left. I couldn't even see far enough to count them all.