I have a number of packs at Prairie Traditions that are designed exactly for that.
Take a look at the Badlands 2200 or 2800, or the Blacks Creek Western Series pack. My personal favorite is the Eberlestock Blue Widow. It is extremely well built and handles more of a load as I can possibly carry.
Prior to my Eberlestock I used an external frame pack. The Blue Widow is far more comfortable and allows me to carry larger loads far easier.
Hey Charlie, I thought you hated horses? :p Actually you make a good point. It's smart not to plan on packing in too far. A moose is a mountain of meat, and isn't something you are going to want to pack long distances even with the best of packs.
If you have read Mike Mittens book he talks about packing a moose for three miles. All by himself! Nine round trips if I remember correctly. I have no desire to even think about such a feat, and 99% of people could not physically do it.