I always kept a small crock pot of alfalfa pellets available in the cage and let the rabbit eat on it's own schedule. Fill the bowl about half way for smaller sized rabbits. Avoid moisture or putting it under the water bottle. Change out the old food if not eaten within 24 hours.
You can let the rabbit have some baby carrots or lettuce to snack on. A salt lick maybe a good thing to have in the cage but also avoid moisture areas with it. Salt is a vital part of an animals diet.
I gave my rabbits fresh clover and grasses occassionally. If possible, I let them get outside and on the ground. They really liked to eat fresh grass. Avoid areas that may have been chemically treated or recently fertilized.
What kind of Rabbit by the way? There are several kinds. When I was a kid I raised 5 different kind. It was a great experience and a good one for a child. I think rabbits are easier to care for than gerbils or hamsters! Much easier to find if lost
Good Luck!!!