These tips are primarily for Americans and Canadians.
John uses the Capital One debit card. This has been fantastic because some international ATM’s charge NO fees with this card, such as the 7-11 ATM’s in Japan. Another important thing to consider are credit card foreign transaction fees. Credit cards aren’t as big in Asia as they are in North America, however, they can be used at most chain stores. Many credit cards charge a percentage for all foreign transactions (typically 1-3%). These fees add up quickly and can be killer over the course of long-term traveling. There are plenty of credit cards available with no foreign transaction fees, even for those with poor credit. I use the Chase Sapphire Reserve card (highly recommended). The Points Guy website can help you find an American card that meets your needs.
We both use the Trailwallet app on our iPhones. This app is convenient for taking care of multiple currencies. It now allows you to export data and it’s good for getting a real-time idea of your spending habits while traveling through various countries.
I recommend keeping a “financial diary.” I keep a record of every major transaction in a Google Docs document so I know what the heck I was thinking when I move money around.
We keep a very simple Google Sheets file with major transactions for future reference. I include things like ATM withdrawals.
I use a simple Google Sheets document to track my monthly finances.