The first thing to remember, the knife is the most basic Outlast tool you can have and has been for  centuries.

Second thing to remember, is that if at all possible you need more than one knife. Minimally, I recommend a fixed blade and a folder.

As the name implies a fixed blade is a one piece knife that doesn't fold or bend at the handle. There are several considerations, these include: what type of metal the blade is; the type of tang; the blade length; blade thickness; shape of the blade; the type of hilt and handle; and type of sheath.

Many knives are coming standard with stainless (actually rust resistant) blades. These usually come with a great edge but some stainless knives are a bear to sharpen, especially in the field. Hi-carbon blades usually take an edge but require care to keep rust and corrosion from fouling the blade.

I recommend a full tang blade. That means the metal from the blade extends all of the way through the handle. The longer and wider the tang the less likely the knife will break.

There are many things a larger blade (this takes in length of the blade, thickness of the blade and shape of the blade) can do that a small knife cannot. The reverse is not true. I don't recommend any fixed blade with a blade length of less than six inches or thinner than 1/4 thickness. Fixed blades of smaller size have difficulty in making shelters, chopping limbs, etc.

I highly recommend a section of the blade be serrated, which makes cutting rope, etc., much easier.  A cross piece guard will prevent your hand from sliding down onto the blade. Such an injury in the wilderness can cripple you.

Stag and wood have made knife handles for centuries. New handle covers (including rubber) give a variety of pros and cons and increased or decreased grip capabilities. Leather has always been the standard for sheaths; again new materials are available and many are actually better.

On folding knives, the Buck 110 Folding Hunter
set the standards for over 30 years. We have many more options today. Those that have a thumb button or thumb hole allow the knife to be opened one-handed. Suffice it to say a survival folding knife ABSOLUTELY should have a blade lock to prevent accidental closure.

Again, I favor a serrated section on the blade. The type of metal for the blade, type of blade lock and shape of the blade are all individual choices based on preference and costs. Don't skimp on price, at the same time - keep it simple, keep it strong and leave the GDI (guys dig it) factor at home. Your life and the lives of your family may count on a quality blade.

Lastly, you need to consider how to sharpen the blade in the field. Light weight diamond sharpeners (including a cone shaped on for the serrations) are usually under $25.00 and they work.

While I prefer a larger fixed blade, you don't need a short sword - a nice Bowie will do very well, thank you. You also don't need a double edged British Commando knife; they are notorious for breaking at the handle. In fact, I do NOT recommend a full double edge on a survival knife. If you have to cinch up on the blade for small work, you'll probably get cut!

Leather sheaths with an adequate retention system are fine; just remember to occasionally treat the leader with baseball glove condition or saddle soap. Ballistic nylon is fine, provided it has a Kydex liner; remember retention. Lastly, I recommend a wrist strap or lanyard.

Wrap the lanyard around the thumb then around the back of your hand. You can customize the strap length for your hand. Even if your hand is wet, you won't drop the knife. AND, if need be you can simply unwrap your hand from the strap if the knife becomes stuck in wood. 

Combat knives are a separate category and I will cover them at another time. Personally, on a hunting or trip I carry a Bowie, a folder AND a multi tool of some type, minimally.

Here's another point, get used to carrying a knife everyday. Remember, NCIS Special Agent in Charge Leroy Jethro Gibbs' Rule #9 - "Never go anywhere without a knife."