This trick works best with a crushed head or more than one clove of garlic. The reason why it peels easily is because of the friction between the cloves in the bowl. The dry fibrous peel is relatively brittle, so all the vigorous shaking inside the bowls helps to break it open along the seams. The clove being slippery, it slides out of the broken peel easily.
Bananas, like many fruits, release ethylene gas naturally, which controls enzymatic browning and ripening of not just itself, but other fruits nearby. Much of that release takes place at the stem, or the crown, of the banana. By wrapping the crown, you slow down the ripening process a bit. For best results, separate bananas and wrap the stems.