Getting fit sux! haha.
I'm with ya on the needing to get fit.
Honestly I kinda had a revelation, I was hiking with a pack in years past etc..., after doing the same loop a few times, same hill, up down up down etc... I was bored, I could keep going, and needed to, but was so bored.
I've always enjoyed running, though haven't in years, my plan is to just get back into running. I'd lose weight, increase my endurance. Even if I never strap on a pack, I'd be stronger than before, I might throw on the pack occasionally and weigh it down and climb some hills etc... just to get accustomed to the weight of a pack, but my main plan is the running.
My suggestions is find something you enjoy, whether that's a basketball league at the local gym, or whatever, swimming, I find an activity is much easier and more fun, than forcing yourself to do some workout you don't enjoy.
p90x will certainly work if you do it, and stick with it, but if you end up dreading the workouts etc... and only doing 1 a week, that won't cut it!
btw let's say im 200lbs, and I lose 20lbs, and strap on that 20lb pack, im back to the same weight i was before, and now I'm stronger and have more endurance, that's a win-win IMO! That's essentially like walking around with no pack before but now I have more strength/endurance.