I can't call it a formula, because I don't really know what I'm doing, but here is how I am currently trying to cover all my bases for feeding my meat rabbits, based on fresh forage year-round (one nice thing about the insular tropics):
Rabbit Salad (serves two adult rabbits--for pregnant does or does with litters, gradually increase ration accordingly and be sure to include plenty of protein)
Ingredients:
3/4 full five-gallon bucket of fresh sweetpotato vines and leaves (main forage base, leaves high in protein, vines high in fiber)
3 to 5 large handfuls of pigeon pea greenery, mostly leaves, with some stems (protein, fiber)
2-4 ti green ti leaves including stems (fiber and diversity of nutrients)
2-4 sugarcane leaves (fiber mainly, I guess, and diversity)
A handful each of several various "herbs" such as: lemongrass, basil, cilantro, parsley, arugula, lettuce, plantain, nasturtium, oregano (for more micro-nutrients and perhaps medicinal benefits--a friend told me that rabbits will naturally "self-medicate with herbs")
A couple handfuls of dried sugarcane, ti, or banana leaves (for additional roughage, entertainment/dental maintenance, although it seems they don't always eat these)
Preparation
Cut and gather ingredients with a pruning knife found lying around that nobody ever uses and an old bucket with a hole in it that isn't good for anything else. Remove any old fodder from the hutches, and then divide fresh ingredients evenly between rabbits, placing fodder on the cage floor at the front of the hutches away from their potty corners. Serve with a tiny handful of pellets in a dish on the side (until the pellets run out, anyway--might as well use them up, having bought them). Clean and refill or top off the water crocks as necessary. Repeat twice a day.
The proof will be in the pudding, or not, when my doe kindles and we see how the bunnies do. I might try to work in a little bit of banana and/or coconut as an energy supplement at some point. Each hutch also has a couple of sticks for chew toys and a mineral salt rock. I'm working with a lot of unknowns since my circumstance is so different from what's covered in most of the literature and forum discussion (plants, climate, production goals), so we'll see how it works out!