Due to increasing food costs and the fear of what they do to our food, we ought to give our rabbits wild foods which wild rabbits eat.
I have been amazed that my bunny will devour small twigs from trees to the last morsel. Bunny loves hawthorn which is so easy to identify in the hedgerows and is incredibly common everywhere. Clip the new young shoots with scissors around the end of March - thorns are not developed or are still soft (but bunny can actually cope with the thorns). During the rest of the year I give bunny hawthorn clippings, 5 or 6 inches long of the new years growth and if there are hard spines I cut them off.
Other trees which bunny will eat are crab apple, birch, willow and hazel. These are not difficult to learn to identify except crab apple which you need to memorise in your local landscape in autumn when the apples are on the tree so that you know where they are for the rest of the year. You can't harm you rabbits with these trees and they really are quite easy to identify.
My bunny lives off cowparsley from the end of March right through to Christmas. You need to be confident in your ID because it has relatives which are poisonous. My approach would be to find a patch which you are confident about and then introduce small amounts to bunny so that there is no ill effect. Near livestock, farmers are likely to have eradicated the poisonous relatives because obviously they don't want to lose stock.
Another prickly customer is the wild rose which bunny devours spines and all.
Finally there are two climbing hedgerow plants which rabbits love. One is the vetch or wild pea which can have purple or yellow flowers and is available from mid summer to autumn. The other is the hedge bindweed which bunny loves and is available mid summer to autumn.
The best approach is probably to add to your knowledge of plants one at a time as you get confident. We as humans have lost so much knowledge that our ancestors took for granted which is a shame: you can't eat a computer chip but humans like rabbits can eat much from the hedgerow and wild places.