since there is a building system and enemies that can roam, how about fortifications and randomly generated area raids? maybe scrap armor to help against taking blows? perhaps a taser baton or horse whips? maybe a farming supplies store?
if you don't know what kind of fortifications, I can help supply some ideas:
- Boarding up windows
- Strengthenable, blockable, and lockable doors to help deter invaders, somewhat sounds like it's possible to make one of the stores into a temporary base
- Electrified fence & gate that can hurt you if you're not too careful
- Wood spike wall, those spikes that're shaped like an X (it sounds inefficient against slimes but can be crafted with long sticks and/or logs)
- Rope-based pulley traps to trip or entangle enemies that'll slow them down