We had, not one, but TWO rings of spell storing and an Ioun stone (3 spell levels) in a game we were in.
1. Paladin(who had been slowly raising an army of Knights) would gift his most loyal soldiers an Intelligent Steed
2. Every PC had a familiar
3. The Wizard cast a spell into it (usually Wall of Force) and let his raven Familiar wear it. Since the raven can speak short words, he can activate the spell and, thus, the wizard could have 2 concentration spells. A bit less strategy when laying it down, since Ravens are dumb, but it worked every now and then.
4. The paladin/sorcerer had shield and that spell that gives you resistance to elemental damage. Two reaction spells that gave him a buff and freed up slots for smites.
5. Use it for improved invisibility on the monk
6. We had no cleric so we would get NPC clerics to put in healing spells during our down time.