I like the idea of being able to boost your stats through gameplay. If you lift weights and eat well regularly for months, you could become stronger! And if you lay around and eat garbage you could become weaker. Your max stamina and rate of stamina regen could be changeable through aerobic exercise. Gives a good reason to live and eat well. It’s not OP if you have to maintain your fitness level, and more fitness requires progressively more and more maintenance, until more would require you dedicating your life to the pursuit, like professional athletes do.
EDIT: Another idea. I’d love to be able to chat with an NPC for a while for a morale boost. Being social is important for human happiness!
DOUBLE EDIT: Are leashes in the game? I’d love a way to be able to keep a friendly dog nearby. Maybe just let me put a collar on it and grab the collar to drag the dog behind me