My grandmother used to make us condensed milk sandwiches, and told us not to tell our mother, who always made sandwiches with beef or cheese and lots of salad in them. To discover that there were jam sandwiches, condensed milk, even sugar sandwiches, was a revelation! As it was that very same grandmother who taught our mother not to fill us up with sweet stuff, but to give us protein and veg, she was being a bit naughty, but I think those were treats that she associated with the war years.
Whereas my mother's idea of a treat during the war years was a banana sandwich, fruit always including a pineapple for my grandmother carted back carefully from wherever by my grandfather, who was in the navy.