I'm not sure there is any one way to target what makes bule so sick in Indonesia. Before I moved here I do not think I had thrown up in over ten years, but in my first year in Jakarta I found myself head-in-toilet on at least ten different occasions. Saying definitively it was warung food, seawater in Lembeh, or ice cubes at the resort may or may not be accurate as there is simply too much sketchy. Have you ever looked at some of the bank notes- especially the 1000 and 2000 notes? So freakin dirty. All we can do, especially when on vacation, is practice good prevention. Here are a few of my favorites:
1. Do not eat food that has not been cooked or peeled unless you are super confident or have washed it yourself. Salads, gado gado, apples etc... are dangerous.
2. Do not eat street food, but if you do bring your own dish and fork. Often the bucket of filthy water used to wash the kaki lima dishes is far more dangerous than the food.
3. Wash your hands with good soap a lot. Take a lot of showers with good soap.
4. Do not sample local alcohol like arak.
5. Ear beer. Always ear beer.
6. Some of my friends swear Bintang is dangerous... I kind of concur. Always go San Miguel if possible.
Cheers.