I made one big mistake in preparing for my Sierra Leone trip last year: I assumed $1 was $1.

Wait, what?

I assumed the exchange rates were based on the value of the dollar, and not the bill itself. I was wrong. A $100 bill in Freetown was worth about 370,000 Leones. However, if I wanted to exchange five $20 bills, they’d give me around 350,000 Leones, depending on how much haggling I wanted to do.

Before I left, I made the assumption that smaller bills would be more useful, since prices for goods would be lower. I carried most of my personal funds in $20 or smaller bills. I ended up getting burned on the exchange rates over the course of two weeks.

That kind of thing is impossible to predict, so best talk to a local before you leave. If you don’t have that option, research as much as possible on the web, with every query you can think of, even the outlandish ones.

If you’re traveling for a commercial or non-profit client, that’s a little easier, as they probably have staff wherever they’re sending you. I was lucky enough to be working for a major NGO, so I had good support on the ground. The agency paid my expenses directly, so they wired funds before I arrived, and I had a healthy amount of cash for most of the trip.

Nevertheless, things never go according to plan. On my last day, I was about $100 short of what I needed to settle my expenses. There are plenty of banks in Freetown, so it was just a matter of making a withdrawal, right? Uh, no.

I have credit and debit cards from several banks, but they’re all MasterCard or American Express. Unfortunately for me, Sierra Leoneans vastly prefer Visa. After visiting six banks, we finally found one with a sign on the door for most every major credit card company in the world. Problem solved, right? No.

Turns out you have to go to the main branch to actually pull a withdrawal from a card. Three hours later, I had the rest of the money I needed.

The moral of that story is two-fold. One, estimate high for your expenses, then add a few hundred more. Two, carry Visa and MasterCard at the very least (caveat: Visa and MC may not rescue you the way AmEx rescued me).

Pay your credit card bills before you leave, so you’ve got as much credit available as possible. Try to keep enough money in your checking account that you won’t need to move any money around while you’re away. However, balance that consideration with the possibility of fraud. Fraud is big business in the developing world, and checking accounts typically don’t offer $0 liability the way credit cards do. Check with your bank to be sure.

Cash is king. The cards probably won’t do you a lot of good on the ground, but if you need to make additional travel arrangements or change existing flights, you’ll need plastic. Also, try to find out if there are limits on the amount of money you’re allowed to bring (in or out) through customs. There’s nothing worse than stuffing $100 bills into your underpants in the bathroom at Harere Airport.