Remember the old knife destruction test series from Youtube? I think Noss had to go into extra innings to break the Busse he tested (was it a Battle Mistress? I can't remember...).
If I had to pick my toughest fixed blade and folder, I'm not exactly sure what models I'd pick, but the fixed blade would probably be a Busse Battle Mistress and the folder would probably be a Cold Steel Pocket Bushman.
If you manage to break a Pocket Bushman AND a Battle Mistress, you might as well give up!
In "real life" I bring a 4" fixed blade and a SAK along with, depending on the season, a hatchet (warm weather) or a Hudson Bay axe and packable bow saw (winter). Ron mentioned a hacksaw... I think that would be a great addition to a "survival" load out and it's seldom mentioned. I have a neat handle that holds a hacksaw blade but is very compact.