Fun erasers are a good idea.
Maybe also cool pencil bags/something to help kids corral school supplies in their desks?
Slightly ornate pens? (they come in glitter, or swirly patterns, or ??)
Decks of cards or card games? If these are too expensive, could you bring in a bunch of age-appropriate card games for the classroom? I think there's one called "24" which is math-oriented, and SET is pretty fun for older kids... There's a younger kid version I can't think of offhand. Maybe check with the teacher on these?
Dry-erase pens for the classroom, and the kids can color during birthday time?
Keychains with goofy things on them? (my 14-year old is carrying one with a rainbow pompom, which I think was a gift from a friend.)
Backpack/bike decorations? Those keychains with LED lights on them?