Many of those methods jeopardize the contents of the chest/door.

How about a key ring to hold all the keys you find?

This also works if you pray to Mellis with a banana peel in your inventory, he will "fill" the "empty container" with banana flesh, and the result is a fresh banana.

How about a skeleton key? Opens any locked door or chest. Would be extremely rare, OFC. Or a Bag of Holding?

Reflecting some things like lightning, fireballs, and healing spells would be cool. Then you could use the old Final Fantasy trick of casting Reflect on a monster before it uses its own healing spell, thus causing it to heal you instead. Or casting Reflect on yourself, and then using lightning or a fireball on yourself and sending it in a random direction.

That's kinda what I meant. Say goodbye to using wands of teleport to get out of jams.

Or perhaps using a wand/scroll of Reflect lets you reflect 1 spell, whereas a ring of reflection or a mirrored shield would give you perma-Reflect status?

Reflect would also be a buff that can be granted by Infuscor.

I was also thinking about a wand/scroll of healing. You can use them to heal yourself, pets, or deal damage to the undead.

A new status effect or two might be nice. What about Reflect?

Reflect would protect you from all spells. Including beneficial ones.