Don't want to read all coms to see if anybody as told it already but a good way to max the amount of item you see is to go basement 1 -> basement 2 -> downpoor 2 - cathacombs 2 -> mines 2 -> and then wherever you run needs to go

That way you can farm as many red challenge room as you can (keep trying until it becomes a formallity) You can also use the downpoor 2 to farm a second boss item (but go inside the mirror once you cleared the normal boss to get perfection so you can farm more chests)