If you get very good at rotating them regularly on abundant, ideal, diverse pasture, you may be able to cut feed by 30%. If you grow them squash, make it winter squash. Mine never liked summer squash. Especially not the overgrown stuff i couldn't find buyers for. I can't blame them. It's probably the least flavorful, nutrient-dense thing in the garden.
Kitchen scraps are good. But piglets will die on you if improperly fed. And a finishing hog wants 10+ lbs of 14 percent corn/soy Mix a day. That's a lot of calories to replace with vegetables, to say nothing of the protein.
All that said, I'm trying to find ways to finish out my pigs with less grain, and think it extremely valuable. Keep the grass tender. Keep the
water clean. Move em. Get them under fruit and nut
trees.