So far, all I've been using throughout the game in terms of spellcasting items are these:
Crystal of Light - quite frequently
Mark of Light - as a backup
Ebony Dai-Katana of Passwall - on occasion, mainly for when a monster is blocking a platform edge and I can't go around
Crystal of Wizard's Fire - only for killing trolls

I've also stockpiled these items, but never used them:
Mark of Ice Storm
Bracers of Light
Bracers of Passwall
Bracers of Force Bolt
Ring of Opening (had this for a while, haven't used it once)

I'm thinking I will:
Keep my Crystal of Light equipped
Keep the Bracers of Light as a backup light source
Equip the Bracers of Force Bolt as my new main troll slayer
Keep the Crystal of Wizard's Fire as a backup troll slayer
Keep using the Ebony Dai-Katana of Passwall equipped
Sell everything else

Is this a good plan? Is there anything important I might want to use other than Light, Force Bolt, and Passwall?