I think the best use of time is physical fitness.

I volunteered as an observer at a search dog training exercise a couple of weeks ago and there were a number of handlers there who got winded just walking a couple of hundred yards up a hill. What are they going to do when they have a hard track over 15 miles of rough terrain?

In a survival situation you need to be fit and healthy and possibly able to construct shelters, swim, travel long distances with minimal provisions, etc. No substitute for being in shape.