When we hear anecdotes about constipation, not going for a week is usually minimum, often much much longer. so then, how many meals can a colon store?

Constipation.: I'm not able to give you a number, but the reason that the colon is able to tolerate not moving for a week or longer is that the stool as it stored in the colon has the water reabsorbed from it. All that is left is indigestible fiber and byproducts of digestion. The body is very efficient at using anything in the food which is nutritious. Eat lots of fiber and drink lots of liquids! Good luck.