The things I can forage are limited to weeds, yard grass and maple trees/leaves.
Perfect! Sugar and silver maples are good rabbit food. You can collect branches and leaves. In winter, you can snip off branches and bring them inside. Place in a little water, a few weeks later they will sprout leaves and you can feed the whole branch to the rabbits, they'll pull off the leaves and buds and most of the bark for a good meal.
Many weeds are good too, do some googling (assuming you don't spray pesticides). Seriously. Dandelion, thistle, goose grass, ragweed, plantain, nettle, violet leaves, and queen anne's lace are all weeds that are good rabbit food. There's lots more.
What just looks like "another green plant" to us is not for them. The different plants taste different to the rabbits and have different composition, so including weeds adds a ton of variety and nutrition to the diet. A dandelion leaf and a clover leaf are as different to a rabbit as a dandelion leaf and a potato are to us.
Collect weeds in an open bin all summer to make your own rabbit salad hay for use in the winter.
Leafy tops from radishes are great, and I've been told (haven't personally tried) that you can grow these indoors from seed very easily in winter. You can also keep a dandelion plant in a pot over winter and harvest leaves for the rabbit.
Most of the things you listed (squash, root veggies) are best as rabbit treats, not rabbit dinners, so growing them to store won't do much good for cutting down on pellets. Think green, think stems and leaves, think the plants and parts of plants that we humans don't eat.
