Cheap food plot.
Using Roundup or another complete kill herbicide is a good idea, but they tend to be a bit expensive now days. Just FYI - after we kill vegetation for a plot we then burn it, but you need to be very careful if that is part of the plan.
Whatever you do you will need to get at minimum bare soil. Use a leaf blower, weed whip, or garden rake to get rid of leaf litter and other debris. If you've got a push lawn mower take it to the plot, set it at the lowest setting and scalp the ground. Be careful of small trees and other brush. That should get you to bare earth - but it might also ruin your mower depending upon what you hit.
Spread some 13-13-13 fertilizer.
Rake up the ground a bit to try to create some lose soil using a garden rake or hoe, this won't be easy - especially on plots 1/4 acre or larger. A tiller really is the prefered method for those on a budget.
Winter wheat is usually pretty cheap, also some white and red clover from your local feed store or grain elevator shouldn't break the bank. Austrian Winter Peas are also inexpensive, but I find deer mow them down before they get much beyond a couple of inches high.
Spread the seed, try to cover it with some soil, and pray for rain.