For my 5 yr old's party, we went with the theme. It was space, so I bought some Starburst and put 3 in each bag, along with 2 snack-sized Milky Way bars. Okay, so the kids didn't get the "space" association, but my son had fun with it. We also bought robot wall stickers at the dollar store and cut the strip of them apart so each kid got one. There were eight on each strip, so that was cheap. (Hint: I wrote "wall sticker" on the back so the parents would know what it was) I also cut apart sheets of shiny star stickers so everyone got half a sheet.
I also wanted a bouncy ball "planet," but I didn't know where to find a bag of them.
My son has gotten mini slinky-type toys, chinese handcuffs, and saltwater taffy when he went to parties before. Pencils and erasers, stickers, etc. are fun, too.