Evan Dorkin wrote this piece about the lack of anything good at thrift stores and Salvation Army stores, and more important, the same things you find at each one, including Paul Reiser's "Parenthood" and the South Pacific soundtrack.
And from Eddie-torial Comments mentions the beat up treasury edition of Battlestar Galactica for $5 you see at each one.
And Mark Evanier (or someone doing a darn good impersonation of him) mentioned the Pogo plastic figures that can be found everywhere, even in parking lots.
For me it seems to be the same 3 or 4 cartoon character glasses from the 1970's that includes Superman. My grandma gave a lot of them to my brother that ended up missing or destroyed. Also the commemorative glassware from each of the Apollo space missions that the Marathon stations gave out or sold. My actual shopping experiences outside of eBay come when I go to Florida at a place called Flea World.
Speaking of which, one time when the family was down there in the late 70's, Seven Eleven had actual superhero glasses for Slurpees, not the plastic ones, but actual glasses. The one I remember was a wraparound Fantastic Four fighting Dr. Doom.
The other main memory I have in that category was the first time we went to Florida in 1974. I had saw and read about Disney World, and was excited about that. The other thing was finding Seven Elevens (none in Indiana, only a few made it up here and were called Super Sevens for a time, but that's another story for another time) and that they had the DC superhero cups. Since there was less than a 2 week window to collect them, I pestered my dad to go every chance we could. The disappointments came when 1) the 3 times a day wasn't met, and 2) finding a checklist that meant it'd be impossible to complete the set, even if a different one was obtained each time. Here's an article I found about it (and the aforementioned checklist link).