I don't know what buffs really stack either, I checked some time ago and didn't find any good answer.

I think Fortitude and Blood Pact shouldn't stack, since they both just add stamina but MOTW should stack with it since it adds all attributes and kings should also stack with both fortitude and motw since it adds % stats which is not the same as them. I think Scroll of Stamina is the same as Fortitude/Blood Pact so doesn't stack.

So in theory improved Fortitude 70.2 stamina + Mark of the Wild 16.2 stamina + Kings 10% stamina would stack.
But fortitude overwrite Blood Pact 49.4 stamina or Stamina Scroll, so they shouldn't stack.

I think Retribution Aura stacks with either of Thorns or Imp pet Fire Shield, but those 2 doesn't stack with each others.

I think resistance from spells doesn't stack at all with each others except if I remember right Demon Armor or Ice Armor stacks with other effects.

I think it almost always is "if they have the same effect, they don't stack", except for retribution aura, healing stream totem and self buffs.