Here is my suggestion for a customization setting and possible challenge. You have 24 hours to get X distance away from your starting location. If you don't, the nuke kills you.

I have no idea how hard that is to code. But the added stress of trying to not just survive but also escape to another location under a time limit makes for a wonderfully exciting game.

Want to crank the stress up to max level? Have the nuke drop at a RANDOM time.