Ozaki O!coat 0.3+Pocket is an extremely thin (0.3mm) and lightweight (9g) case that is made using polypropylene.
The back of the case is leather textured and it has a card holder slot that holds one credit card (at most two). If you don’t like putting your credit card there, you can use it to hold reminders written on small pieces of paper (which is what my mom is doing) and I find that is a great idea! If not you can use it to hold up name cards or your EZ-Link/Octopus/Oyster card.