Well, not too much grain. Don't want him to develop urinary issues.
Goats can get sturdy on alfalfa, but they LOVE weeds/scrub the best. They're browsers, not lawn mowers.
You'll get a lot of different ideas on what to feed here. As has been noted occasionally, there are at least as many ways to raise goats as there are people raising them.
My goats get good alfalfa hay, alfalfa pellets, COB, BOSS, beet shred, and free-choice minerals. When I remember, they get baking soda.
We grew some mangelwurzels this year, and I wish I'd made it a point to be more careful growing it - as in more careful to grow MORE. The goats LOVE it!
I also just planted a Fall crop of turnips and a fistful of early-crop corn seed I found in a box. The goats enjoy the turnips (tops and roots), and even if the corn doesn't produce grain, they like the leaves/stalks.
Oh, and they also like apples, raisins, bananas....