As a daycare teacher, these "fake" graduations are more important to the children than the adults. To the kids, they are transitioning into real school with new friends and celebrating that they won't be seeing their daycare teachers anymore.
I would suggest socks from the Target Dollar Spot, if you can find them. Perhaps to wear on the first day of Kindergarden.
My daughter got her first webkinz for graduation. Big deal for her since her big sister already had some. I waited until she was starting to read to get her one. She still remembers which one (of her 25, 3 years later) was from pre school graduation