Joie, I am sorry I did not see this before.
If you’re going to S.E. Asia, EAT EVERYTHING COOKED. Don’t even eat fruit uncooked. That is my number one suggestion. Boil water that you drink.
If you can afford it, eat only at upscale restaurants. They should still be reasonably cheap for you. Don’t decide to eat at little shit holes, because that’s what they will be: shit holes.
As far as supplements, I would take my stand-by HCL Acid and possibly some Lyposhperic Vitamin C.
I would take along some good anti-diarhea medicine. I know that some people here are going to warn you off of these, and normally so would I, but you’re going to be on vacation and wanting to enjoy it, so….
I’m going to be honest with you, even with these precautions, you will probably get some stomach upset during your travels; however, I think the above recommendations will help. At least, they help me when I go there.