What a load of utter rubbish the answer in the link on the first posting is!
Snap was a very popular childrens' card game consisting of twenty-six pairs of cards depicting characters, jobs etc. All the cards were dealt out and players laid one card face up on the previous one. When two identical cards were played, the first to spot the pair yelled "Snap", and picked the pack up.
You were 'out' when your hand was finished, and the one who scooped the entire deck obviously won. So whenever two identical things appear many still call "Snap" bacause of childhood memories.
I dare say if you looked you would certainly find a pack of "Snap" cards today.