The one and only reason I started exercising was for hunting out west. I've gone through highs and lows of physical fitness over the past 7 or 8 years. Too much cardio without a weight program will get you a heck of a cardio base, but no strength to get you up the hills. Too much weight work will get you strong, but quick to get winded. It takes a good mix. There are 2 different ways that I found to work almost equally well. I can tell a few differences between the 2, but not a whole lot.
In 2014 a group of us decided to go to CO for elk. This would be my 2nd trip and I knew I needed to be better prepared cardiovascularly. I did nothing but run and ruck. I dropped 25lb over 6 months. When we got there I was good to go with no load. Hauling a pack up and down the mountain dang near killed me. I had the cardio, but not near enough leg strength to keep me going. I got fatigued, I started compensating for weaknesses and just transferred the pain to other places. Not an overall good experience.
In 2017 I was getting ready for an elk hunt in WY, as well as my first marathon. Leading up to my October hunt I may have missed a dozen days of running total from January to October. I was also doing a 5x5 weight lifting program 3 times a week. I found that I had a great cardio base, and plenty of strength to get my up the hills. I didn't bulk up because of all the running, I didn't lose muscle and weight too fast because of the lifting.
I just did my first sheep hunt this past August. I wasn't running as much due to plantar fasciitis issues. I was still running some, but shorter distances more infrequently. I did, however, supplement my cardio with HIIT. The gym I go to does HIIT, Crossfit, and similar type workouts at lunch. We also made it a point to do stadiums once a week. I would put on a weighted pack, walk the 1.5mi from the gym to the track, do a few miles on the track and stairs, then ruck back to the gym. Again, I had a good cardio base and good strength.
I'm not saying either is the best for you. As others have said, the sooner you start, the better. Start now, find something that works for you, and stick with it. The sooner you start, the sooner you can figure out what you need to be doing.