When your child can follow simple directions, have him pick up all the food he throws on the floor, and place it in a small portable trashcan/sack. It doesn't deter him from throwing food on the floor since the cleanup is still fun, but it is a start to learning there are consequences for his actions. At 20 months, we had our son "help" us put laundry from the washer into the dryer, and he "helps" put his toys up into the toyboxes. If I am cleaning something that involves wiping, sometimes I give him a washcloth so he can feel like he is helping to clean too. It gives him a great feeling of accomplishment, and is great training for future chores.