Rabbit pellets are the staple food in almost all rabbit's diets. Feed companies have researched and formulated pellets to be a complete rabbit feed in which no other feed or supplementation is required to successfully raise rabbits.

But that doesn’t not mean that you can’t give them other treats
Carrots, Timothy Hay,
Rabbit Treats--apples
Chew Sticks--willow branches, apple tree cuttings
Good For "Gut"--blackberry leaves, raspberry leaves, dry oak leaves, kale, dandelion leaves, oats (whole or rolled)