bring (or buy when he gets there) some pepto bismol tablets or similar over the counter treatment.
if he doesnt have a strong stomach: dont use ice - in anything. dont eat street food. Even when eating in a "good" restaurant he should hope the staff have washed the food and their hands at least once that day. be very careful to only drink from NEW and sealed bottles/cans. wash hands.
oh, and bring (or buy when he gets there) some pepto bismol or similar treatment.
pretty much the same advice given to anyone travelling to any other developing country.