When I went to India for the first time, I was lucky to have small bills on me because the day I landed, the Indian government said they were banning the use of certain big bill denominations! This was in a supposed effort to stem corruption.

For the duration of my trip, I saw never-ending lines at banks across the country, of people trying to exchange their larger, discontinued bills for legal tender. I was able to get by with what I had for a while, but I still had to be very mindful of my cash supply for a while since ATMs were out-of-order across the country due to overuse.  Eventually a tour guide facilitated a trip to the bank, so I didn't have to ration my dwindling cash supply anymore. But even the bank visit still required lots of paperwork and waiting. It was truly unexpected.

I don't expect the local government to announce such a sweeping economic change every time you travel, of course, but having a variety of bills in either the local currency or your home currency to exchange upon arrival is always good practice. 

• If possible, bring some cash in the currency of the country you're visiting with you before you arrive, in both big and small bills. 
• If you can't get local currency before your trip, at least try to bring some cash in your home currency.

Have you ever traveled without any money?