Haven't seen this posted anywhere yet so thought i would post it.
there is a glitch if you r using cabal rider. Buy as many potions as you can doesn't matter what kind they are. Then start dropping them on the ground
,make sure you have auto loot on for this, the bot will pick the potions back up and put them in stacks of 98. this leaves a lot of room in the inventory fill it however you like. Hope this helps someone.