When Therapist shows a Grizzly Bear Quiver, that means you had a Grizzly Bear Quiver in your fort and that it was assigned to that squad position's uniform because that dwarf is expected to carry ammo. It also means that quiver was available for use and could be pathed to when it was assigned. The dwarf will only attempt to equip the quiver after they have equipped their crossbow.
The wool backpack, this is assigned to the dwarf because they are expected to carry food supplies. Somewhere in your fort there is or was a wool backpack, probably from trade or visitors, since dwarfs cannot make them from wool. I see none now...
I don't have Therapist on this machine so I didn't see which dwarfs are not picking up stuff or what stuff they are not equipping, but failure to pick up an assigned item usually indicates a uniform conflict (unable to wear high boots over shoes, or conflict with mining/woodcutting/hunting, but I am guessing you checked for those, easy enough with Therapist), or the item became inaccessible after it was assigned (it fell into a pit, into 7/7 water, or is locked behind a door/gate... the item was accessible when it was assigned. Example, military dwarfs are dying in the caverns, a dwarf is assigned a dead guy's quiver, you close the gate and the dwarf can no longer path to the quiver). In general, dwarfs consider uniform-equipping to be a high-priority job. They will go get that stuff unless they need to eat/drink/sleep.
Your dwarfs are mostly set to wear uniforms over clothing and to wear uniforms off-duty, so they should not be picking up and dropping most equipment except when they are upgrading gear or getting more ammo (but I do not know if they pickup and drop backpacks/flasks when going on/off-duty since I don't let them carry them in my forts). So, which dwarfs are problem dwarfs?