Just 1 bomb, 1 potion and 1 oil equiped at the same time, and you can change the type of bomb, potion or oil when you are out of combat.
Would be fun because if you think when you accept a mission or dungeon or raid, they always explain your enemy, this is the problem the big "DRAGON" did this, this "PIRATES" or this "CULTISTS" did that, this "ANIMALS" are causing this damage. So you always know what enemy type will you be fighting in that quest/dungeon/raid so as a Melee Ranger you will have plenty of time to choose what types of potion, bombs, oil you are going to use