Resolutiion has a total of 12 usable items, and 11 permanent upgrades. Weapons, like the Calmer, are used purely for combat; some items, like Chromatic Aberration, are used purely for progression; and some others, like Stardust, can be used for both. In addition, there are 3 alternate weapons added with the Craftsman update that must be swapped for an existing weapon, as you only have 9 inventory slots.