Stuff yourself means to pig out which describes a situation when you eat a lot so that you can't eat anything else. Here it means to eat in a silly way which connotes that you cannot do your activity well or think wisely due to eating extravagantly.

Stuff something means to put a lot of something into something. Like "Stuff a teddy bear with wool" Stuff Ourselves with food. Stuff the clothes into the drawer. Stuff the pillow down the side of the bed