If you can't complete your order right now but want to save the products in your Cart, you can easily do so as a registered user. To do this, you need to register as a user (here are instructions), and once registered, log in on the website. This way, you can design and save products in the Cart, where they will be saved indefinitely (until you complete the order or remove them from the Cart).
You can even switch devices (mobile, PC, tablet...) and, every time you log in with your registered user account, the products will be in the Cart exactly as you saved them on another device. This way, you can add more products or edit the previously added products before completing your order.