Documentation.

There’s an amount of information and paper-based items that you will need to carry on you. Consider ways to protect hard copies from water. Ziploc bags do fine, or go big and buy something from a camping store.

I also recommend putting all typed info and scans on a USB stick labeled with a red cross and your name. This is one way to offer a backup, and though an imaginative stretch, any information in an electronic document can be translated with software from English if necessary. There are also times when you may need to email or print out a copy of these items. If you are bringing a mobile device, save reference information in the form of scans or pics on your device. 

Identification. Protect your passport and other personal ID. When you need to have these items on your physical person, I recommend waterproofing. You never know when you might find yourself in the middle of Songkran Festival or invited to lunch down at the river.

Chiang Dao, northern Thailand.

While you're at it, leave copies of your name and contact info in your bags and luggage. These may be the only means of connecting lost items to you if external tags have been removed (it's happened to me...)

Personal Info. Make copies of the above items of ID, along with your relevant medical info, health/travel insurance, flights, accommodations, travel routes, local contacts, and emergency contacts. This is especially important when travelling solo. Put all these paper documents in a big Ziploc-type bag.

A word on health/travel insurance: I have had a fantastic experience with World Nomads. They have covered me for missing luggage when I needed to replace riding gear and tools for an impending race, and also covered me for a two-day hospital stay about three weeks later. The claim process was extremely easy. If not them—someone else. There are a number of health and safety risks when travelling in this way, so protect yourself.

Passport photos. You can often find local photographers to make these up for you, but I recommend having a number of these in a few common sizes on hand for visa applications and such.

Money. Authorize any bank or credit cards for use in the countries you visit beforehand. ATMs are everywhere, and usually offer the best exchange rates. You can also take a major credit card into banks worldwide and get a cash advance with proper ID. US dollars are still very useful in everyday exchanges, and especially in one-dollar denominations for certain countries. Research beforehand to know how much to carry daily, and what to expect to pay for things you will need.

Maps. If you have paper versions of these, protect them as well. 

Entertainment. Some of this may be in electronic form on your mobile device, but consider also packing a journal and pens or pencils. If you desperately need that feeling of a physical book to read, try finding a used book store in town catering to backpackers and tourists. 

I need a journal and Harper's.