Moine:

I don't know what kind of backpack you use, but I favor external frame type. They give you more breathing space between your back and your pack, and I like the ability to add stuff to the exterior of the pack on the frame (camera tripods, walking sticks, axes, machetes, ski's, ski poles, add infinitum.) and not feel the pack slumping over from the weight.

If you have an internally framed one or a rucksack that you carry on your back, one trick is to cut a car seat ventilator (those seat accessories with the spun steel or plastic coils used to allow air flow when sitting on plastic or leather car seats.) in half and attach it to that part of the pack resting on your back for better air circulation.

Good luck!

Bountyhunter