I don’t have one.

The second smallest size binder clip, with maybe 6 or 7 cards in it. It’s maybe 8mm at its thickest and 6mm in most spots and is the footprint of a standard plasticized card.

Tiny coin purse that fits my cards. I have a couple of bank cards and 3 loyalty cards

I have two. One relatively small one that I take with me everybday:
Regular debit card
AmEx
Drivers License
Radio operator certificate
Airline bonus membership card
Some cash in in whatever is the local currency

The other one is larger that I usually keep in my backpack:
Passport
Two seaman’s books
Vaccination booklet
Various visa-related paperwork
Some cash in frequently used currencies

My wallet is 6 cards in a rubber band

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It’s more than a centimeter, less than an inch.

But I haven’t carried it with me in this millennium. It stays locked in the briefcase I also don’t carry.

I just carry my ID and a CC, loose in my pocket.