I always keep 200 dollars rolled up in my shoe or other hiding spot for an emergency.
It's enough to get you into a hotel food and buy a cheap phone while you figure out how to deal with whatever problem happened. Have a plan for if your card gets eaten by an ATM or lost.
Never had to use it, as I never had a problem.
ATMs everywhere but currency exchanges can be a bit dodgy in the boonies. Sometimes they won't take old bills or ones with marks or writing on them. Bring new ones.