Card-only travel works perfectly — until it doesn't. Card declined, ATM unavailable, infrastructure outage, theft of one card. Three forms of payment kept in separate places handles almost all failure modes.
The three-form approach
Primary debit card (Revolut, Monzo, Chase — no FX fees). Backup credit card (Halifax Clarity or Chase — no FX fees, different network). Small cash (£50-100 equivalent in local currency, ideally in $20s or local notes).
Where to keep them
Primary card in wallet. Backup card in different bag or money belt. Cash split: some in wallet, some in luggage as emergency reserve. Photos of all card numbers and CSCs stored securely on phone.
Test the system before leaving. Check FX fees on each card. Confirm international travel notifications set with banks. Ensure backup card has sufficient available credit.