Kill everything with Roundup then burn it if you can, give it a light disking, wait a couple of weeks and kill it again.
We have put in food plots with a pull behind ATV disk and they come out just fine. Planting clover or other small seed perrinials doesn't require much ground breakup. Matter of fact all you really need is some slits in the soil, that is why veritcutters work in yards. The main thing is to get to bare soil.
But as the proud owner of a new tractor with a 6 foot tiller on the back, I can tell you a tiller will work just fine. I used ours on ground that hadn't been turned in the last 20 years, had cattle on it for the past several, and was pretty pugged up in some places. The tiller made short work of it.
Ideally plowing and getting good soil turn over would be preferred, but since this is a food plot on not a crop field for production you can get by with less work and still have something productive.
“There are two spiritual dangers in not owning a farm. One is the danger of supposing that breakfast comes from the grocery, and the other that heat comes from the furnace.”