Don't get in shape, stay in shape. Do something you know you will do the rest of your life. Since I usually hunt out west every other year, I used to get in shape one year and then get out of shape for a year and then repeat. Finally, I decided it was much easier to avoid the swings.
Moderate diet, lots of cardio, as much weight training as you like and pack work on hills.
Train for your game. If you are packing 50# over mountains, use that pack to prepare. Personally, I keep it fresh. I do 3 week rotations of cardio, weight training, dieting, and taking it easy. Overall, as long as I do something all the time, keep my weight reasonably low, and hike some trails every once in a while, I feel pretty good. I'm 42 now and in the best shape of my life.
Somebody asked me today what my overall end goal was for working out. I told her it was "To live healthy until I was 75 or 80 and then die in the woods," I wish I would have added "dragging my grandkid's deer out."
If I do, I hope they leave me there.