Some credit cards let you put a travel itinerary in their records, to reduce the chance of this happening (if I recall correctly, American Express will do it for you automatically, so if you buy a plane ticket to Rome, they'll know charges from Italy are probably good).
But yes, multiple SEPARATE funding sources and cash are a minimum when traveling, even within the US imo.
Multiple bank accounts, even if you operate primarily with cash, are a requirement for normal living. You always want a backup, preferably isolated from the original.
But yes, multiple SEPARATE funding sources and cash are a minimum when traveling, even within the US imo.