You have some good advice here. The only thing I can add is to buy a pack that will stand up to some abuse (aka heavy duty fabric and buckles). My DW has a weak back after a high school ski accident so I prioritized on going ultralight for her backpack. Unfortunately, the pack we choose for her was indeed light (~2 lbs) but I popped buckles multiple times by lifting it in the wrong place. The material is gossmer (silicon impregnated nylon) and is pretty flimsy when hiking through brush.

Good luck,

By circumstance my DW and I will also be going to REI this weekend to replace the pack I mentioned above. wink

Cheers,
Nemo
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You must be the change you wish to see in the world - MK Gandhi