Douglas Harper's Etymology Dictionary
s'mores
snack treat, 1937, from childish contraction of some more, as in "I'd like some more of those." S'more as a contraction is recorded by 1887.
Wiktionary
s'mores
n. (plural of s'more English)
Usage examples of "s'mores".
Two hours later, I'm down at the local galaxy-class grocery store, in Bulk: a Manhattan of towering Lucite bins filled with steel-cut rolled oats, off-brand Froot Loops, sun-dried tomatoes, prefabricated s'mores, macadamias, French roasts and pignolias, all dispensed into your bag or bucket with a jerk at the handy Plexiglas guillotine.
I made coffee and treated myself to a strawberry Pop Tart, feeling righteous because I'd resisted the S'mores Pop Tart.