What To Look For
There are many types of pocket knives available, all suited to specific uses. When purchasing a pocket knife you should first make sure that it has the tools you desire. Perhaps you need a can opener or pair of pliers. Once you can be sure that it covers the tool set you seek, then look to other options. Look for a blade that locks into place for greater safety. Select a metal that holds an edge. Weight may be an important factor, particularly if you are a backpacker looking to shed a few extra ounces.
A common pitfall when buying a knife is to end up with one with a nonexistent or poor locking mechanism. Having a blade that locks into place should be a high priority, since it is both safer and easier to handle. However, just having a locking blade is not enough. Try and open and close the knife with one hand. If this is difficult, consider a different blade. You'd be surprised how much ease of opening and closing matters.
Where To Buy
Pocket knives should be purchased at an outdoor outfitter. Look for stores that will allow you to handle the knives out of their packaging. Knives should not be purchased from a dealer, unless you trust the person selling to you. Sometimes knives bought out of their packaging will be dull or of inferior metal.
Pocket knives can vary wildly in price. A quality locking blade can be had for $40 or so. However, the price is likely to go up quickly from there. Many quality multi-tools, such as those made by Leatherman or Gerber, can cost upward of $80. Knives with assisted-opening, which will snap out smoothly, can cost even more.
Comparison shopping is best performed in your hands. Try out how different blades feel when holding them. You'll want a bit of heft, to give it a sense of durability, but also a lightweight feel, so it doesn't weigh down your pockets. Open all tools and test the lock blades with one hand. Most knives will come in a few varieties, with different blades. Make sure to check out serrated, semi-serrated and a normal blade to determine what's best for you. Another area of comparison is the blade's tip. Some are pointed, while others are flat to prevent accidental stabbing or to allow use as a pry bar.
A good sheath can help a lot in storing and carrying your knife. You will also want a wet stone for sharpening and mineral oil for prepping your sharpening stone.