To take a few elements from a certain game, brewing potions from secondary items you could possibly collect in your travels, either in game or sending surviving members out to forage, a certain member has to be a tracker e.g. So you can collect a whole host of different things in game, and out of game, get them through treasure collected, wandering monsters killed or general loot at the end of the game.
Then you can look up a table mix the ingredients you've collected and on a will roll you make a potion.
Just a little fun idea, not to complex either if you ask me.
Potion ideas...
Potion of bendy arrows - Heatseeking shot.
Potion of gloop - next attack solidifies the target but deals 0 damage, further damage breaks the solidified goop.
Potion of the spirit form - can only be damaged by magical attacks
Potion of hovering - can make a Pop-up-attack style shooting attack
Potion of "The good-ole-switcheroo" drink and replace target model with another friendly aligned model.
Potion of feather leap - Can jump across a flat surface double the move distance.
Potion of detection - can cast spells upon anyone within 10' without needing Los when normally needing Los.
I'm out...