In stock at our local Japanese grocer are a lot of these fun kits for making your own erasers. They are about $10 each, which is a bit more expensive than my average craft fling, so I only bought one kit to start with - sushi of course!
It's really pretty simple though. Spray the mold with some water to prevent sticking.
Anyway, repeat with other colors to create your sushi, and then to "cure" your eraser, submerge it in water within the box and microwave. Since my microwave was twice as powerful as the microwave chart given in the instructions, I halved the cooking time. (about 2 minutes for me)
"Hey babe, watch me vulcanize this rubber."
@_@ Okay, maybe not.
Anyway, once everything is done, cut out the paper bits to finish the scene.
While not as pretty as the box, the finished erasers still exceeded my expectations!