You will want to bring enough money for a few meals by yourself, the expenses you incurr while traveling, and any souvenirs that you might want to bring home with you. Also, to have some money for personal items such as the occasional candy bar or coca-cola or other things that you would normally need when you are home is a good practice. This kind of thing varies in cost depending on the company and coverage you apply for. You will be traveling in third world countries where sanitation is not as stringent as it is here in the United States. Therefore you will have to be conscious about the things that you eat, drink, and touch.
Some remedies seem to work better for some people than for others.
If you have a preferred precaution or remedy, you might want to check with your doctor before you travel. The practice that seems most successful is the maintanence of personal hygene. Some people are more sensitive to shots and to diseases than others. I think it is best to face the facts. There are a whole bunch of nasty diseases floating around the world that are health and life threatening.