Fluffy lives on a diet of water, cat food, and (optionally) live mealworms. We make sure that there is about a quarter cup of each of the water and cat food in her feeding bowls every night. She does not always eat all of it and she is able to self-regulate how much she needs to eat. She will eat more if she has been running more.
Hedgehogs make their mess while they are running. We keep Fluffy's wheel in her litter tray. She has been trained to use the litter tray, and will often do so while running in the wheel. The litter we use is great at absorbing the smell!