Bones to Bananas turns all normal bones, big bones and monkey bones in the backpack into bananas, which heal up to 200 life points each. This spell can be used to stay in combat without having to use a bank for a long time. Bones to Peaches is a higher level alternative.
The spell has 50% chance of not using any runes if a player completed hard Lumbridge achievements. The advantage lasts 10 times each day. The required runes must still be in the backpack to cast it even if they are not used. This does not work when trying to make tablets.
With a full inventory of 27 bones (and a stack of nature runes), there is a profit of 1,754 coins per spell assuming a mud staff is equipped and that runes were used.
Only considering the cost of nature runes, the following table shows the profit per 27 bone of different tradeable bone types when turned into bananas, worth 314 coins each.
When the spell first came out in 2001, it was called "Bones to bread" and required no nature runes.
This is, in all probability, the spell which added to infamously unlucky pirate Unlucky Jenkins's resume of bad luck (It turned his ribs to bananas, which were promptly ripped out by monkeys).
The spell and Bones To Peaches are possibly a reference to the song "I Like Bananas (Because They Have No Bones)" by The Hoosier Hot Shots. The lyrics of the song state: "I don’t like your peaches, They are full of stones, But I like bananas, Because they have no bones".
If you have bones in your inventory, but none that work with the spell, you get a message that states "The bones you're holding aren't suitable for bananification."
Bones to Bananas was once glitched so that its tooltip included an Armadyl rune alongside the required runes, however the spell did not actually require an Armadyl rune to cast. This was fixed in an unknown update.