I'm new here, been playing the game for about a week. Figured I'd make my suggestions before I forget.
About a week now I've been running around and dieing. So I was thinking why not implement some sort of Physical Stats system. Start off average and as you play your physical strength will increase as you defeat Z's, allowing you to kill them much faster/easier with heavier weapons. It would be a very slow developing skill but that would ultimately add just abit more to work for in the game.
Same general idea for stamina and agility as strength, since you do a ton of running in this game at least to start. Why not make it so as the game progresses you can run faster and for longer.
The fat system is pretty basic, you are too fat you can't run, but the skinnier you become the more often you will require food to regain your energy.
Health is just cause I'm going annoyed of dieing for reasons unknown to me, If I'm low on blood I'd like to know, if I get hit again I'm going to die, something that will give me an idea of exactly what is going on.
Now the eating habits, from what I can tell this game is real time.... so why am I hungry every 5 mintues? Make it abit longer you eat and maybe 30 minutes later you are hungry, I've died of starvation multiple times cause I can't find any food. When I had barely gotten thirsty in the game, with all the running you should become thirsty more often then hungry.
Well I think thats enough of my random ideas.