There seems to be several items you can unlock at random
I have found:
mage's acolyte
crude ring
void ring
I am wondering how many more there are, which ones are unique, which one would I want for a perfect playthrough, etc..
so far i haven't been able to equip any of them although i admittedly haven't made it very far yet and
only noticed it when i started a new playthrough
also it seems like the item may be randomized at the start of the game instead of just before opening the chest but im not sure on this