I love these little hats at No Fuss Fabulous that are made out of little Reece's cups and a square or chocolate.
I also have an idea for a serving dish by using black bowl for the cap and a black plate glued to the top and some sort of tassel or maybe just a fruit rollup rolled up for the tassel. The challenge is going to be finding a black plate that will work - while spray painting the bottom bowl is ok, I don't like the idea of serving food on something that has been spray painted.
This is made out the cup off an egg carton for the cap, a piece of cardboard painted with acrylic paint and a piece of yarn for the tassle. This would made a cute decoration or even be used to decorate a graduation present for little to no cost (I usually have all the stuff to make this around the house).
Over at Little Birdie Secrets, they have a tutorial on how to make a felt graduation cap