Skip shellfish, even if cooked. Don't buy food from street vendors. Make sure cooked food is served very hot. Sometimes it happens in spite of precautions. The most important thing is fluid replacement - bottled water, flat soft drinks, sports drinks, or tea will help.
Drugstores usually sell packets of oral rehydration solution.
Or you can combine 12 ounces of boiled water with a pinch of salt, baking soda, and two to four tablespoons of sugar. If you've brought your own medications, take them. But if you have a high fever or don't start to get better in 48 hours, get medical help if possible. If you're close to a U.S. consulate, someone there may be able to direct you. You should know how to do the self-administered Heimlich maneuver, in case you start choking on food when no one is around to help.