I agree with you: Too often survival has come to mean some new, expensive piece of kit or some clever procedure.
I'm not sure how to develop mental toughness on your own. The military has been working on this for years. For example, the basis of ranger and parachute training is development of the "press on, don't quit" attitude.

As far a the physical attributes, a checkup and correction of medical prolems is the initial phase.

The next item for many of us, is a proper weight control program and your doctor may be able to help you here. I can't/won't reccommend a particular diet, but eating and lifestyle changes which gets you to and maintains your weight for body mass is crucial.

The physical training is the third aspect of your physical development. For those of us who lack the money, time and access to a formal, supervised gym, we need to develop our own program.
Expensive home exercise equipment isn't necessary.
I developed my own routine by going to a couple of manuals:
"Physical Training"- US Army FM 31-20
"Physical Conditioning"- US Army TM 21-200
"Physical Fitness, The 5BX Program"- RCAF (Canadian Armed Forces)
"Fighting Fit, The IDF Guide to Physical Fitness"- Col. David Ben-Asher
"The Royal Marine Commandos Fitness and Survival Skills"- John Watney
There are a number of other guides out there.

The critical factors are:
Start right now!
Begin small and work up.
Do it every day.
There are opportunities for variety. For instance, use an exercise cycle in winter rather than a mountain bike, long walks or hike varied with runs etc.
Again, keep at it.
GOOD LUCK!