Whether you are engaged in general outdoor activities, climbing, hiking or canoeing, it is always a wise choice to carry an appropriate outdoor knife with you. Even if you never need it for safety reasons, a knife is always good for a variety of everyday tasks. From the outdoor cooking perspective, my personal recommendation is a Victorinox, which has most of what you need in cooking: knife, fish scaler, corkscrew, can opener, etc.
Knives with fixed blades
Since there are no moving parts, solid knives are stronger and more durable than folding knives. Fixed blades are recommended for, for example, filleting fish, cutting and chopping vegetables. The main disadvantage of knives with a fixed blade is that they require a holster that is often hard to keep clean from bacteria. Select a knife with a plastic holster, it is easier to keep hygienic.
Many (but not all) folding knives have several blades of different lengths and types. This provides greater versatility. But folding knives are not as durable as knives with fixed blades. If several blades and features (scissors, saw, etc.) appeals to you as much as me, consider a Swiss Army knife or a Leatherman multi-tool.
There are three common types of blades: straight, serrated and combination of straight/serrated.
Ideal for use around the camp kitchen, straight blade is a good general cutting tool. It is also relatively easy to sharpen and it keeps its edge longer than the serrated blade.
A serrated blade can be distinguished by teeth that are embedded in the blade. Though not as apparent as the teeth of a saw, a serrated blade is much more efficient than a straight blade to cut through, for example, a fish. But serrated blades become dull more rapidly and are difficult to sharpen. Round files, usually of several sizes, and a lot of patience is required for sanding.
A straight blade near the pointed end and toothed blade near the grip; this combination offers the best features of both worlds. Let your intended activity determine the blade type, or if you really need the versatility, choose a knife or multi-tool with several blade options.
The most popular blade materials are alloy, carbon/steel and stainless steel. The blade of carbon steel is easy to sharpen and it maintains its sharpness longer than the blade of stainless steel, but it rusts if not treated with silicone wax or used regularly. The blade of stainless steel does not rust, but it requires more work to maintain its sharpness.
Knives for hiking/camping
In outdoor activities you want to keep the weight to a minimum. A good outdoor knife is small and lightweight, but sturdy enough to withstand heavy use, as the activities you practice outdoors can give the knife more wear than in your home kitchen. A blade with both sharp and serrated edge can be most beneficial here.
When you buy a proper knife, you will be amazed at all the uses you find for it. Whether you need to cut through the vegetation or make a barbecue stick, cut vegetables or fillet a fish, the knife should be an integral part of your equipment.