Make all “cash” in the form of plastic coins from recycled PET bottles. Different denominations have different shapes so humans can easily tell them apart. Embedded in each coin is a Mu chip (link). It is an RFID chip that only can be read from very close up (1/8 inch at most) if one uses the on-chip antenna. That way nobody can read through your pocket how much money you have.

Different from current concepts that suggest such chips as a safety feature in this idea the chip IS the coin. The RFID chips don’t carry a serial number, but an ID that indicates the value of the coin. Higher value coins could also have a small sliver of platinum embedded. It serves as proof of ownership so you can get a replacement at a bank if the plastic burns up (must show your ID and do paperwork in that case).

Such coins would be cheaper to make in large quantity, but harder to fake in a backyard operation because it takes a major outfit to make the chips. Suspicious individuals could carry a key ring gadget that allows reading one coin at a time. At a store the customer would throw the coins on a reader tray and the cash register would automatically sort it out and give change. The mechanism to identify coins in vending machines would cost a tiny fraction of the mechanical systems in use today. People with metal allergies would not have crumbly skin any more, and best of all: no more sagging pockets filled with pennies.