You need to be in that Arrange-menu. Then you should choose the option at the bottom "Customize". That way you can arrange your items yourself. Another way you can get it quicker is choose the selection "Battle" that way all the items you can use in battle are closer to the top then the once you can only use in the field or weapons. Ofcourse with the last option you still have to go past the potions and phoenix downs, but they are closer.