I've handled a lot of moose in my life now, most of them we were able to get wheelers or other vehicles right up to, but the handful that I had to put on my back taught me a few things even after getting in 'good shape'.
1. Stamina is more important that strength. I once had a relative who came to help me pack a moose a mile through a swamp back to the wheelers. He was on the wrestling team, he also power lifted at the time. We put a hind quarter on his back and he made it maybe 400 yards before he gassed and asked for something lighter. I ended up getting both hinds out that moose.
2. Get the hinds out first! After processing the bull you are going to be whipped already, you will never be fresher than you are right at that moment, so get the hinds out. If something bad happens and you can't get the rest out, at least you got the biggest pieces of meat out, and all other trips will feel better compared to those.
3. A good pack frame makes all the difference in the world. You can be superman, but if your pack or pack frame sucks to wear its gonna be a real crappy day.
4. Rubber boots suck to pack moose in. I've done it, it sucks, i'm prone to rolling ankles. The last few times I knew I was going to put moose on my back, I put the good hiking boots on, got my feet wet, and praised the lord that I had them on instead of rubber boots during the pack out.
5. Mentally tough is more important than physically after the first load out

. There is nothing more sobering than getting that first load to the wheeler or camp, feeling your shoulders rejoice after shedding the weight, then realize you have to do that 3 or more times. I've known guys who got the first load out then 'went to get help' or waited 'until tomorrow after they rest' because they didn't think they could do it. There are other critters out there that would love a moose feast for free, time is of the essence. Eat a snickers or take a snort of that Fireball whiskey, and get back in there.