Here are the fundamental characteristics that you need in a knife:
1. Full Tang
2. Non serrated edge
3. Single edged
4. Drop point
5. No longer than your pinky to outstretched thumb
6. Carbon vs. Stainless steel
Now let's address each of these issues in detail.
The metal of the knife should reach from the tip of your blade all the way to the hilt of other end of the knife. If your knife isn't full tang then you have the chance of breaking the knife when you split wood. One of my students had that experience last summer.
I would be remiss if told you I always carried a full tang knife. When I first joined the army a couple decades back I rushed out to find the biggest, baddest scariest knife I could find and started to carry that on my webbing taped upside down for quick access. It had a hollow handle that had space to keep as sorts of cool-guy stuff secreted away. Needless to say I quickly broke that knife in half during normal use. Not only that, I soon realised that I didn't like carrying extra weight during those long road marches.
Shortly after that I switched to a Gerber style. They don't make the one I had anymore but this is close. It had a kydex sheath that double locked so when I jumped out of the aircraft it didn't accidentally slip out in midair. With my luck it would have hit someone and given me some medic work to do once I landed.
Bottom line. Have a knife that will not break when you need it.
Non Serrated Edge
If you need to saw something, use a saw. Most of the time the serrated edge is close to the handle which is right where I want my carving edge for articulate work. Also, serrated edges are a pain in the patookus to sharpen. Some knives have a serrated edge on the opposite side as your cutting edge. Don't buy a knife with double edges. That leads us to the next issue.
Single Edged blade
If you use a knife with a cutting edge on the back of the knife, one of two things will happen. Either you will cut yourself or you will not be able to use your knife to it's full potential. Your choice.
You need a strong thick back to support your cutting edge. This part of the knife will be abused and treated like open season to a whack-a-snake competition (this is a redneck thing). You cannot split logs with your knife unless it has a strong blunt edge to pound on.
The point of your perfect bushcraft knife should taper equally into a point that lands right in the middle of your knife blade. Less than desirable options will be the fillet knife point that sweeps away from the cutting edge.
You want a point that allows you to use your knife as an awl to carefully dig a round hollow into wood. The point should only have one side sharpened. There are options out there that provide a knife point that has two cutting edges to it. We covered this problem already.
No longer than you pinky to your outstretched thumb
Your body is amazing. It knows a lot of things about bushcraft that you never knew until now. It knows the exact measurements of loads of bushcrafty things. One of which is the length of your knife.
20 centimeters is the length between my pinky and thumb when stretched out. That means that I need to choose a knife that is around that total length. Anything longer than that is waisted space and weight.
Again, I have to mention my younger days of folly. As a private, not only did I have large knives strapped to various places on my kit, I decided that I really needed to have a full sized Kukri knife as well. The blade alone was over 30cm. It was heavy. I carried it for a few weeks before I began to see the error of my ways. If there was a task that warranted such a large knife (there wasn't) I could use my camp axe or folding saw. Both of which are much lighter than the Kukri. Sure it looks cool and it is fun to chop things with, but quite worthless overall.
Carbon vs. Stainless steel
Here is where I open up a fury of opposition. There are carbon purists and there are stainless vigilantes. Let's look at the bottom line.
Carbon is the better metal by far. It holds an edge much longer, it is easier to make an edge and it will last longer. The downside is that maintenance is more difficult than the stainless especially in the climate here in Ireland.
Stainless has it's virtues as well. You can throw it in your ruck for months at a time and not worry about it. You can make an edge on it but you must resharpen every few hours during extensive work.
Both are about the same cost. We sell both options during our bushcraft courses. If you keep a nice film of grease on the carbon blade you can prolong the inevitable rust from starting. Despite my best efforts I find rust on about half of all my carbon blades that I keep in the classroom. I keep most of them here in the cabin where it is warmer and less humid (sometimes).
My personal favorite knife is the Scout Knife from Tops. It was a knife given to me while working at the Tracker School. I plan to make these when I have my forge set up are running. The size is perfect for my hand at just over 18cm. The blade is about twice the width of the Frost knives we sell in the school. I find that extra width easier to carve with. Plus, the knife is large enough to lash to the end of a staff to make a spear.
The frost knives that we sell are by far the best option for a first bushcraft knife. They are only 3/4 tang. That is the only setback I see. And at the cost of only €10-15 it is affordable by most.
The most important aspect of bushcraft knives is not the type and style of the knife.....it is the wielder of the knife. If you want to learn knife safety and bushcraft applications for your knife get some education. Talk to the Irish Bushcraft Club who go on monthly excursion to the wilds of Ireland. Get some 'dirt time' with your knife and find out what works and what doesn't work.
The final point I have is a lesson in non attachment. Your knife is your tool not your identity.
More information can be found at www.ipna.ie.