CardNinja Like The Nest, above, I didn’t know what to make of the $20 CardNinja at first. But after trying it, I can see its appeal. This thin, stretchy pouch adheres to the back of your iPhone (or any smooth iPhone case) and provides a place to stash some cash, an ID, and a credit card or two, letting you leave your wallet behind. When empty, the pouch hardly adds any bulk to your phone, but it can fit a lot more stuff than you’d expect—and its stretchy material keeps that stuff from sliding out. The CardNinja is available in black, gray, or purple, and its adhesive is non-permanent, so you can remove the CardNinja if you ever get tired of it.