The ice could be made from tap water. Hot, freshly prepared foods are safest. Look out for any foods left out on serving tables or foods containing raw meats or seafood. Try to stick with fresh fruits and vegetables that can be peeled. Don't eat foods made from unpasteurized dairy products.
Salads are especially risky.
Don't eat foods from street vendors. There's no way of knowing when or how that food was prepared. In general, a rule to keep in mind is, if you aren't sure, avoid it. You might want to bring some antibacterial soap along with you for your trip. One way to prevent traveler's diarrhea is to take anti-diarrheal medicine tablets every day during your trip and for a couple of days after you get home.