As far as regular feed is concerned, I feed my rabbits Albers Double Duty, this feed really puts some conditioning and bulkiness on a rabbit with that I also add All-Breed (feed for all types of animals) and COB, this is a good mixture of feed for show animals.
I feed my rabbits Timothy hay in the winter adds some bulkiness on the rabbits also. In the summer I usually feed grass hay, mainly because they hardly eat any of it, and it gives them something to do, because they like to just chew on it.
Although your rabbits probably say "be generous" feed treats sparingly! There are a wide range of treats for rabbits. But the ones I like best are Carrots, Parsley and Apple.