You can only wear so much, and for the spellcasters, the Rings of xxx Magic are hugely important. I'm also a great believer in items that boost multiple resistances (there are too many individual attack methods to cope with resistances individually), and items which enable hit point and spell point recovery. I think in this game you can get items "of Plenty", which boost both hit point and spell point recovery, but IIRC they are very rare.
One thing, though, unless you have a Thief or a Ninja in your party, your Disarm Traps expert is certainly going to need an item to boost Thievery if you want to prevent things from blowing up fairly regularly.
It's also hugely beneficial for every character to be able to GM a combat skill. The advantages for melée fighters and especially spellcasters are huge, not only for their access to the top spells, but for the more effective way that all spells function, right down to the most basic ones. This is why the druid fails so spectacularly in this game. After he's made the black potions, he's not quite dead weight, but he cannot match the other party members in any specialised areas.