Cataclysm: Dark Days Ahead is a free to play downloadable game for PC, and has a port for mobile on the google play store (the control scheme for mobile is pretty atrocious though. They had some buttons for some keyboard keys appear on the bottom of the screen when they’re relevant, but not all of them.)
It’s a top down zombie survival game that’s got a lot of features. The parts that we’re interested in are obviously the stomach, which can be stuffed with food or fluids, and the weight, which can increase and decrease.
Also, speaking as someone who’s never modded any game before, it looks pretty easy to mod and it’s open source.