SHOULDER STRAPS:
They should not bear more than 20% of the weight most of the time. They are mainly to keep the top of the pack from "falling backwards". Padded hip belts carry the rest of the load.
STERNUM STRAP:
This is used to take strain off the shoulder straps OCASIONALLY, not all the time. They also pull the pack in to prevent it from moving around in steep climbs or descents.
LIFT STRAPS:
Most good packs have them and they balance the pack, pulling it in toward the shoulders when tightened for climbing steeper hills.
Descents can be made more comfortable by loosening the lift straps a lot and letting the pack top lean back, again, for better balance. Good backpackers ae constantly re-adjusting pack straps for comfort in varying terrain.
WAIST BELT: It needs to fit YOUR hip structure. Packs that have side tension adjustments are nice, otherwise belts need to be tailored for different hip shapes, especially for women. **Walk around the store for 30 minutes with a fully loaded pack to see if it truly fits you.**
This belt must be fairly comfortable 100% of the time. It should have decently large side pockets to store items you will need while walking like compasses, sunscreen, monocular, etc.
The main idea of a padded waist belt is to transfer weight TO your big bones (pelvis and legs) and OFF your spinal column. Kelty was the first pack maker to make this idea a reality in the '60s.
FRAMES: The best hunting packs have good internal frames. External frames are not recommended unless you absolutely will use it mainly for carrying out quartered game. Internal frames are lighter and move a bit with your body for greater comfort. Plus they are much more maneuverable in brushy or heavily wooded areas. All frames main job is to transfer weight to the padded hip belt but they often provide for back ventilation, pack shape and attatchment points for hipbelts, shoulder straps and definitely for lift straps.