Chick starter is the best thing for the first few weeks. Or if it's too cold to spend some time outside, my chicks love a big piece of grass sod in their brooder. They can practice foraging and eating grass/small bus. But I don't usually give treats very early on. Usually only corn scratch when they are older and sleeping in the coop when it's very cold. And veggie scraps, but only after they are living outside full time.
I would definitely suggest a buddy or two if you only have one chick. Chickens need and love companionship : )