Personally I don't think a grab and go hard case of rifles should even be considered. Animals being hunted, terrain, max possible range and other factors come into play as are specific state game laws. Take PA for example. If you brought an AR or any semi-auto for big game you'd be SOL because they're not legal (yet).
Now for a pack that's another animal. There are a bunch of things that you can throw in it that can be used for every hunt. Examples: first aid kit, flashlight, fire starter, knofe, sharpener and a host of other items. Things like binos, spotting scope etc can be added depending on the hunt.