A wee bit Heath robinson,
https://www.ebay.co.uk/itm/261997643628
It’s a common-or-garden sd card holder. Can be found cheaper…
Using pliers, gently prise out the rubbery innards.
These can be replaced with adhesive backed credit card holders. Room for emergency cash/ tea-bag.
https://www.ebay.co.uk/itm/182430556210
In time, I’m going to find out if any of the metal rfid credit card holders will fit inside.
https://www.ebay.co.uk/itm/131904481169
You’ll need to attach a wallet chain, as the wallet is naturally buoyant and will float away down the nearest brook/ stream/ river.