I use the same Clarks "comfortable" shoes for walking the streets of Saigon as I do for battling with commuters at Victoria Station in London. Same socks too. Not sure I really want to be walking in sandals with some of the gunk that's around.

Just wear what's comfortable. It amazes me the way I see backpackers walking around Saigon (where there's a cafe on every corner and often airconned too) with a super-large bottle of water hanging off their backside in case they have a sudden dehydration issue. Its a kind of status symbol. Just as having the LP guide with the most ruffled pages....

Simon's sticking to cities which are pretty civilized. I wouldn't worry. I wouldn't swallow tablets in the expectation of being sick either.

I used to carry Imodium with me (not on my person, but back at whereever I was staying) "just in case". But I got fed up with the things forever expiring unused. Have taken 2 of them in the last 14 years. I bought them locally and could have done without them. You can find Boots/Watsons in much of Asia, or their equivalents - and on Simon's OP, I'd suggest it is only BKK where he's facing any risk. Last serious poisoning I had was in the UK a few Christmas's back when I reheated some Turkey on "defrost" instead of "high". Didn't want to miss what was about to start on TV so ate it anyway. Boy didn't I pay a price - took me a week to recover. So mistakes can happen anywhere.

In the end, some stuff just puts me off. If you force yourself to eat food that smells odd or looks strange 'cos its local and part of the tourist experience, it will probably make you sick. No need to feel guilty about fitting in the odd baguette, pizza or Starbucks+chocolate cake if it keeps your system going.