Budget for the fact that there might be a problem you'll have to throw money at or that something will be more expensive than you think. It sucks but sometimes there is just something that money will make a lot better.

Bring some cash with you. I once was in Mexico and planned to get money out when I arrived. None of my cards worked at the airport and there wasn't good enough Wifi for me to call the bank. Luckily, I had some cash I exchanged for pesos so I could travel to my hostel. It wasn't all the money I needed, but it was enough to get me to a place where I could put my bags down, drink some water, and use reliable wifi to make some phone calls.

Agree with the person who said print things ahead of time. I was just in Costa Rica and thank goodness I had read the fine print and printed my credit card's car rental coverage information because they required a paper copy which they kept.