Kinda crazy idea I think but hear me out
what if each class and armor had a skill/potion/scroll (unlimited use) you can use on the potion slot? Like, health potions are useful in a lot of places early on but no one really buys them for what i know, so what if the warrior for example had access to it? You open the inventory, click on warrior and there's a button to equip the potion on the class itself, this could open up some use for "weak" classes
I used health as an example because I think a warrior would carry a few potions, but some classes may carry other things
like wizards carry a scroll for mana regen, rogues may carry a trinket that adds a passive instead (as a rank 10 passive because it lacks one) etc..
And also armors, like a basic robe you buy very early on having food to give you a bit of a boost, the ninja armor giving you a bit of haste, and vampire armors give a bit of lifesteal and so on...
this may call for a buff on consumables to make them worth using but some of them already have pretty good effects, like the wasabi Holy Wasabi which gives you 2x damage to undead, so a healer's cross might only give you 1,5x since it won't disappear on use, health potions restore 100% of weapon dmg as health instantly, so an armor's potion might just heal 50 to 75% of weapon dmg and so on
classes with rank 10 passives won't have this resource but can still use ones granted by armors
this is a way to make it worth looking for a armor not only by the looks, may also bring more variety to play with since you'd have that extra thing to mess with, which in return will make the combat a gain bit more deep and encourage players to use classes they wouldn't use before, this already appear on AWE enchantments and boost items so my suggestion is just "adding more of it" I think, make that 1 armor be worth the slot.