This is nothing major, actually, but well worth noting. Once you have the Slingshot, you can now return to the Bazaar in Skyloft and find Beedle’s Airshop flying around. Shoot the bell on it with your Slingshot to be able to shop here.
This will stop you from filling the Wallet soon enough - trust me, it’ll happen enough in some places to get almost infuriating. Here’s an example: when I opened a chest once and found a Gold Rupee … and already had maxed Rupees.