Essentials:
Rabbit pellets, but NOT gormet Petco/Petsmart colorful pellet mixes
Timothy hay, grass/orchard hay
Water (unlimited)

Optional but often recommended in moderation for health benefits:
​Dried papaya or pineapple to aid in digestive health
Black oil sunflower seeds (supplement)
​Flax seeds (supplement)
Whole oats (to reduce diarrhea)
Banana (but not the peel)
Papaya and pineapple (very good for digestive health in moderation)
Shredded wheat (to help weight gain or to increase appetite)
Parsley or cilantro (helps Charlies or rabbits with megacolon)
Stale bread (helps clear up diarrhea, also helps with Charlies or rabbits with megacolon)