Every long-distance backpacker and thru-hiker should carry a knife. It’s one of the most essential tools you can carry. A lot of new hikers tend to carry bigger knives than they need. We found that the best knife is one that can carry out multiple functions and still remain lightweight.

Buck Knife
Weight: 5.7 ounces (162 grams)
Blade Length: 4.5 inches
Pros: large fixed blade
Cons: expensive, weight, no extra functions like scissors, tweezers, etc.
Buckmaster Knife
Retail Cost: $60
Swiss Army Knife
Weight: 0.74 ounces (21 grams)
Blade Length: 1.5 inches
Pros: lightweight, includes tweezers, scissors, toothpick, file and screwdriver
Cons: short blade length
Swiss Army Classic SD Pocket Knife
Retail Cost: $18
Summary
If you plan on thru-hiking or backpacking you should really carry a knife with you. For most hikers, the affordable and lightweight Swiss Army knife with a lot of useful functions is the best option. There is little need for a large, heavy knife when you actually get on trail.
If you are traveling by plane you will need to check your knife in a bag. TSA does not allow knives to be carried onto planes, no matter how small they are!