Im trying to find this movie; the man and his wife had stop at a store and when went in the trunck to get something out of the bag a snake bit him. Later own his started getting slimey and then it grew an eyeball and his habd eventually turned into a snake

Maybe Sssssss (1973) - IMDb (http://www.imdb.com/title/tt0070622/)

Or

The Bite (1989) - IMDb (http://www.imdb.com/title/tt0094929/)