Cash
These days, most of us, at least Americans, are used to paying with a credit card, or now, our phones acting as digital wallets. This is convenient, but always at the risk of being lost, stolen, or useless. I’ve had cards suddenly stop working even within the US when, for example, you drive too far in a day on a road trip and purchase two states over from where you live trip a fraud alert- on a Saturday night. To avoid those headaches, I always bring enough cash to take care of at least my basic life needs for 24 hours so I can sort out other forms of payment.