There are just four things I consider to be the most important for any long term traveler.
1. A really good pair of shoes. I've destroyed four pairs of shoes since the start of my trip, only my German made, Lowa trekking boots have made it with me around the world. I'm currently rocking Red Wings boots, model no. 875. The company is based in southeast Minnesota, its over 100 years old and truly understands how to make a boot that will last just about forever. Everything is manufactured in the US.
2. A really good camera. I started out using a Nikon D90 and several lenses, but something went wrong with the auto focus sensor. One expensive repair job later and it still doesn't focus correctly. I decided to switch systems and bought an Olympus OM-D and after several months of use, I'll never go back to a DSLR again. The camera is weather sealed and along with the kit lens, is water resistant. The system has matured extremely well and has almost a complete set of super high quality prime lenses.
3. No smart phone can beat the simplicity of a good notebook. My favorite little notebook is made by Zequenz. I find them better designed than the overpriced Moleskins. Each notebook comes with a little magnetic bookmark. The binding of the notebook allows you to completely fold it backwards. They now come in various colours and are available with lined, grid or blank pages.
4. The best source of good entertainment, a good book. At one point in my trip, I was carrying around four paperback books. Good books were just hard to find and I was very reluctant to give any of mine up. After a visit back home, I decide it was time to get myself a Kindle, one of the best investments I've made. There's now an updated version, known as Kindle Paperwhite, with a built in glowing surface.
And one more thing...
5. I've ditched my 75L backpack for a roller case. However, if you are going with a backpack, skip the top loading ones and buy yourself one that unzips from the front. It makes packing and unpacking so much easier and saves yourself from the major hassle of having to dig all around your pack to find that one clean underwear.