Some of these have probably already been said, but here's what comes to mind:

- pencils, crayons, markers, drawing paper, construction paper, coloring books, workbooks (Dollar Tree has these all the time), playdoh, small craft kits (fun foam, etc.), stickers, stamps, any school supplies, bookmark, flier from the library on their summer reading program, coupons to local attractions & kid friendly restaurants (roller skating, swimming, bounce places, museum, aquarium, fast food, pizza, etc.), pool toys, beach ball, ball, frisbee, sand pail & shovel, pinwheel