Best all around is to just remember to include fiber in all your meals. Veggies, nuts, seeds, whole grains, that sort of thing. You won’t have much trouble going when you’re ready to go. In the U.S. that also means not buying much take out / fast food junk, hardly any of those foods have fiber.

If you meant “quickest” then you might be thinking of foods with a laxative effect, a quick drink of black coffee cold brew concentrate works for me. Something I discovered by accident when in a rush to get my day going one morning LOL.