Bananas are primarily used for the Summoning to create Fruit Bat familiar. One can cast Bones To Bananas on an inventory of bones to turn them into bananas. Set up one of your quick presets to withdraw 27 bones and 1 nature rune. Cast the Bones to Banana spell, which will cause the whole inventory to turn into bananas. Open the bank, click the Quick Preset, and repeat. When playing at maximum efficiency, up to 780 spells can be cast per hour, for 21,870 bones. To maximize efficiency, add the Bones To Bananas spell to "1" on the action bar. Click on the banker, press 1, and 1 again, and repeat.