Caroline beat me to saying stickers or mixed nuts. You could print out coupons good for "one ice cream cone", "one night of staying up late" or "one pass for not doing chores today". Treasure hunt clues would be fun leading up to finding their Easter baskets or to finding a bigger gift. You could also fill some of them with riddles or jokes if the kids like them.
I know that the Dollar Tree and Michael's had mini pens and pencils that might fit into on those eggs. There are erasers, too, but I always end up throwing them away because the kids never use them. The Dollar Tree also sells in the toys little capsules that you dissolve in water --they contain different shaped sponges like animals or boats...etc. You can also find the capsule that contain wash cloths. Bath fizzy tablets might work if you can find small ones.
Let us know what you decide to use. I'm always looking for ideas like this for my kids, too.