You can use an iPhone wallet such as Solo Wallet to hold some items along with your iPhone 4. But if you don’t want to add too much bulk on your iPhone, the following hanji iPhone 4 cover may be more suitable for you.
Hanji or Korean paper is a sort of traditional handmade paper made of dak (paper mulberry), and the hanji iPhone 4 cover is especially mixed with natural materials as charcoal, mud, and coated with natural lacquer for eco-friendly and durable construction, so the protective cover can effectively protect the back of your iPhone 4 or iPhone 4S from scratches without adding too much bulk. As we can see from the images, the iPhone 4 cover also features a practical pocket in order to hold your credit card or some cash, and the custom cutouts allow you to take out your item from the pocket, and the iPhone camera is accessible.
Hanji iPhone 4 cover is available in 4 colors including bark, charcoal, mud and gold, each one is priced at $10 USD. If you’re interested, jump to connect design for more details.