I am not sure, never tried it for more than a few hours during gas alerts over in the big sand box. most of are food is stored in the bus-racks on the back of the turret. We had large cooler a grill and boxes of MRE and 20gal of water.
20 gal of water for four people, i'd guess it's safe to assume one could, if needed, stay inside for something like 3 weeks. Not that you'd have the strength to pick up the gun round by then but hey, you can't have it all.
The water is stored on the outside of the tank. Thre is not that much room for a great deal of food and water on the inside. I would keep 2 canteens inside the tank most of the time and maybe a MRE or two for myself. Again most of the food stuffs is stored on the outside.