In general for gigantic fights (in addition to being careful with positioning and area control), potions of speed will help significantly. Unlike casting Haste (with a spell slot or scroll), you don't have to worry about losing concentration. And, unlike in tabletop D&D, BG3's version lets you do more than just take a single extra attack.
Additionally, a lot of the "elixir" potions are extremely OP -- and they last all day!. The Elixir of Bloodlust is particularly great, especially when you have a lot of enemies to fight, because in addition to some temporary HP, it gives you an extra action whenever you drop someone. (And, again, an action you can do anything with. That's crazy good!)
