I did sometime last year and have been patiently waiting for Spring since! Here's what I came up with for my nephew and nieces.
For my nephew: A growing, glow in the dark skeleton, a spinning top, a Lightning McQueen pad of paper, a Phineas and Ferb sticker and a little squirting animal.
My niece's wasn't too different: a spinning top, a Mater pad of paper, a Phineas and Ferb sticker (not pictured for some reason!), a little squirting animal and a pretty necklace.
All these small items fit inside a somewhat larger egg (it's not huge!). All my items came from the Dollar Tree, including the eggs. I will send these out soon and let you know how they fare in the mail!