There are a variety of types of backpacking trips that all require different gear, but in general you are going to want a set of basic things:
You will of course want a backpacking backpack. It is important when buying a pack to know how much stuff you plan to bring with you regularly, so you can adjust for size. You will also want to get straps around the hips (a normal backpack will not do). The most important thing about buying ...