Personally, I don't tend to think of "survival knife" as a category as much as I try to determine if a given knife is well suited for wilderness survival use. Sort of how I don't think of a firesteel as a survival fire-starter but as a fire making tool that would be useful in a wilderness survival situation (for example).

So, in a wilderness survival situation, I'd hope my knife could handle batoning and other, more heavy duty, wood processing tasks easily. This would allow for both cutting branches & larger pieces of wood for shelter building and fire making. Basically, it should be able to handle all my normal camping tasks, but be strong enough that I could do some of those heavier tasks with it if I didn't have the hatchet or saw I might normally have with me during a planned multi-day trip.

Really, a lot of my criteria in selecting a knife that can serve this role have been shaped by Doug Ritter's articles on this topic. So my criteria would include:

• Fixed blade
• Single, plain edge & without a saw-back
• Full tang
• Moderately sized (around 4 or 5 inches)
• Drop point / spear point blade
• 1/8" - 1/4" thick
• Half guard

Also, like chaosmagnet mentioned, while this makes a lot of sense for the wilderness I'd find myself in out here in Western Canada, other environments might have other considerations that may add or remove criteria from that list.