Sometimes there's a lot to learn from the most innocuous activity.

I do some farming on weekends and try to keep up with people who have that core strength and endurance that most farmers seem to have. I really think that this kind of activity is beneficial in that it trains the body in ways that might not be available in a gym, although once you've done the activity then you might be able to mimic it in the gym.

E.g., using a cutlass or machete to clear bush for a few hours really teaches you that there are muscles on your arm, back and abdominal region that you had no idea existed or were so weak.

Away from the farm, I go for walks carrying a medicine ball (10-15lbs) alternating from arm to arm both under the arm and on the shoulder. Sometimes it gets so that I have to use both arms. Usually I do this for about a half-hour walk. I discovered this when I nearly died trying to carry a pumpkin (about 20lbs) from the back of the farm to the boat wearing long boots - a distance of about 1.25 miles.

This exercise gets my arm, leg, back and abdominal muscles working really good and imparts a strength and endurance that's hard to mimic in the gym. A lighter weight could be used for beginners, people who are not fit or are elderly. Note that this sounds similar to persons who train with a backpack but it is significantly different. Please give it a try.

I really think that, while it is not the "cure all" of exercises, it is an important exercise and one (of many) that is relevant to survival situations.