Do research and find a charitable organization to donate to. I always stuff my backpack full of items to donate. It'll make you feel good to give back to the country you're visiting and will leave you with lots of extra room for souvenirs.

Unfortunately, “Delhi belly” is hard to avoid. Prepare yourself ahead of time by packing meds like Pepto and Imodium, as well as some kind of powered rehydration drink mix like Gatorade.

You never know when hunger will strike. I like to keep a stash of granola bars in my day pack. They're a lifesaver on long bus rides.