Spoiler: Mine is Ice Cream!!
I ask the question often to land managers and landowners
The answers differ wildly from location to location, ironclay peas, clover, brassicas, radishes, turnips, pears, acorns, corn, soy beans…etc, you ask 50 land managers and you’ll probably get at least 25 different answers if not 50.
When I ask the same question to scientists, biologist and the people who actually study deer, the people who cut their stomachs open and sift through every single piece of vegetation and nut and identify it and weigh it and write scientific articles about it, the answer is always wildly different from what the landowners/land managers say.