If you do any exercise in addition to your tree work or forestry work, etc, you'll be fine. No need to go off and buy all these supplements and pay $X per month for the latest fad workout programs.
Supplements are a waste of money. If you're eating a healthy diet, you're getting all the "supplements" you need!
And don't listen to the BS rule about eating once ounce of protein per pound in body weight daily. Too much of any vitamin or mineral or essential amino acid is not a good thing. Proteins are large molecules and can easily damage your kidneys when consumed in excess.
A good, well-balanced diet, exercise 3-5 days a week and you'll be good to go.
I've been getting in shape to take my pack test at the end of May. It's at 7,000' elevation and I'm currently at 4,500'. Jog a few times a week, hit the weights twice a week. Push ups, crunches, pull ups, lots of stretching the rest of the week. Get some hiking in at 8,000' on the weekends.