The Vaultskin City has a maximum capacity of 10 cards (8 in the dedicated card slots and 2 in the secret slot). This is a pretty great all-round capacity especially considering the size of the wallet. You can even fit 3 cards in some of the slots.
Along with the 4 card slots on the inside, the wallet also has a secret slot located on the inside of the banknote sleeve. This is actually a really nice and ingenious way to add additional functionality to the wallet and works really nice for easy access.