Bone spear rings are a known glitch in the inventory system, generated mostly in the BF.
There are a few books / manuscripts required for quests, but in most cases once you've read one you do not need it. If you keep anything that looks unique, you can drop it before leaving for the next act, or once you get there, since AFAIK there are no cross-act quests.
Take the obvious stuff with you between acts: backup equipment, crystal bag, teleporter stones once you have them (only in act 2 and 3), loot to sell, etc.