[Bardp1999]

You can make it more complicated if you want by introducing spell slots and how certain spells/effects stack and don't stack based on what number slot they occupy, but as a general rule of thumb there are 3 kinds of regen - Racial, Spell, Item. So basically you can have Iskar racial regen, fungi tunic, and lets say pack chloroplast all rolling at once. As pointed out, the fungi staff just gives you a spell regen click so it will stack with everything besides Druid and Shaman regen spells or other items that have a click regen effect.