Nothing. I asked my GP, but... Unless you are planning on doing some tourism on the countryside before surgery or having sex as a farewell gift to your penis (I know of somebody who did it), you will mostly be moving between your hospital room and the supermarket / mall, and you will spend most of the time after surgery on an aseptic environment (the clinic), or again in your hotel room (Chett made me stay for 10 days). There will be low chances of catching something
Just stay away from street food vendors, as a lot of companions have ended with food posisoning. You could get a mosquito repellent since Zika is a thing in Asia.
The thing I would recommend is getting a flu shot. You are going to spend 12 hours in a massive plane crowded with people, plus the airport connections. That's where you would have the highest right of catching something.