Cards fit easily into Czech city travel, while cash remains useful for small counters, countryside stops and the places where a minimum spend or temporary terminal problem appears. The important moment is not choosing card or cash. It is deciding who converts the money when a terminal or ATM displays two currencies.
Give the wallet three layers
The second currency is DCC
A familiar number can be the expensive one
Dynamic currency conversion translates a Czech purchase or withdrawal into the cardholder's currency at the point of sale. It should display both totals, the exchange rate and any markup. Declining it does not cancel the transaction; it normally keeps the charge in CZK for later conversion by your own payment network or issuer.
The ATM logo is only the first check
Match the machine to the network on your card, then read every fee screen. A bank-attached ATM offers a staffed institution and a clear location if the card is retained or cash fails to appear. Your home bank may still add a withdrawal fee, foreign-exchange charge or cash-advance treatment.
Withdraw useful denominations, not a trophy note
A machine may dispense 1,000- or 2,000-koruna notes. Use a staffed supermarket, hotel or larger restaurant to make change after a real purchase. A reserve made only of 5,000-koruna notes is technically cash but practically poor change for a tram-side kiosk.
Euros create a second rate at the counter
Some tourist-facing shops accept euros, but they choose the conversion and can return change in koruna. Paying directly in CZK keeps one amount on the receipt and makes price comparison easier. Save euro notes for the euro area unless a clearly disclosed Czech offer is genuinely better.