I enjoy these thought experiments...
Priority would be avoiding injuries and not leaving yourself too tired/sore to perform when called upon. So nothing near your max, no TGUs, no heavy loads of any kind, no long runs or rucks in places you aren't sure are safe, etc.
TBH much of the 'training' you'd need day-to-day would probably be just surviving/scavaging/running away/fighting as needed. But assuming you have some stable and safe set-up (indoor or outdoor) though, I'd do some combination of:
Some mobility work.
Easy running or rucking.
Pull-ups and push-ups.
Swings and snatches.
Light to moderate barbell work: squats, deadlifts, presses.
And maybe something like some sandbag work or some GPP Crossfit-lite programming.
For me it'd look quite like the Novocaine format that's been talked about on here I think.