I buy a lot of the kids stuff at resale kids shops, but don't have a lot of luck at general resale places like Goodwill. Although, I always walk through and have gotten an rei brand bike for Carrot for $10. A leap frog table and push walker for pumpkin for a few bucks
I always look for Pyrex w lids because I freeze a lot of food. Cool fabrics I intend to craft with.
Today I am also looking for more silverware for lunches (everyone takes a lunch everyday & takes cheap stuff, because it gets misplaced too easily). Decent school pants for Carrot-I love that she plays hard, but she gets holes in her pants all the time.
For me, I always look at the shoes first. Usually I don't find anything, but every once in a while I find something like a pair of Nike Frees for $10 or cute boots. I always look at the t-shirts to see if I can find anything fun, and sweaters. I stopped looking for clothes for the kids - everything decent goes to the plentiful consignment shops around here.
I look for good wooden toys, and books for everyone.
I haven't been true thrift shopping in ages but I will garage sale and go to consignment sales. Most of that is for kid stuff. I generally look at clothes, toys, and books. I'll also look for 1950s pink pyrex.