Vegetables. Any kind.
Also, here’s a counterintuitive tip: if you’re going to eat beans, take fiber pills as well. The soluble fiber from the pills lessens the grief from all the insoluble fiber in the beans.
fiber pills as well
Do you mean something like “Bean-o,” or could Metamucil (psyllium husk fibres) work? Just about everyone needs more fibre in their diets, after all.
coleslaw specifically, with the raw veggie form, not the ultraprocessed one with stuff in it. just put it on a egg wrap and eat it after microwaving it a bit, gaurenteed bowel movement the next day if not super “blocked”, just not cooked veggies as they have little effect since the fiber would be destroyed by the heating process.

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.
broccoli
I’ve always loved broccoli, and a lot of folks hate it, so…
Roast your broccoli, people.
Toss it with a little olive oil, salt it, and bake at 400 or so until it’s browning.
It adds a depth of flavor you wouldn’t expect if you’ve never had it.


