Well, it would be more for a knife I could abuse a bit if I had to. Say, truck breaks down, and I need to cut something I'd rather not cut with my little pocket folder. Or if I need to cut something bigger than my little knife can handle. More semi-emergent situations, rather than planned engagements.
Bottom line recommendations: Opinel #10 (modified to taste) or Buck 110 (if you can deal with hollow ground clip points) or the Buck Ecolite 110 (if you like the Buck 110 but weight is an issue).
So, I guess 4 things or choices come to mind right away.
1) Grind - I think the basic choices available in larger production knives are convex (Opinel), scandi (Mora and the like) and convex (Buck and pretty much most production knives). Closely related to this is the overall thickness of the spine of the blade from thin (Opinel) to thick (Buck hunting knives).
2) Blade Profile & length- Drop point, clip point many others... 3"-4", 5", more?
3) Slip joint, locking folder of fixed
4) Weight - heavy to light
I really like having a larger back up knife around. I frees me to use a smaller, more civilian friendly pocket knife for EDC use with the security of knowing that I can tackle larger cutting tasks when/if the need arises.
I have a Buck 110 (and 112), a 5" Case fixed blade (316-5) and a modified Opinel #10 (reprofiled to drop point - picture below). Here are my own thoughts, which may not apply to you. I've not owned a scandi ground Mora.
I can't sharpen by hand well and rely on a system like the Lansky. I can get reliably shaving sharp results on both the convex Opinels and concave Bucks and my Case. I don't maintain my Opinels with a true convex edge at the cutting edge. I'm not sure if/how I would use a Lansky with a Mora type blade. Something to think about. I want my back up knife to be sharp.
For cutting brush and branches (mostly using the bend and slice method), I have a slight preference for the Opinel. Something about the convex grind seems to make it bind up in the wood less often. This combined with the larger handle makes it a bit easier to cut brush with; at least it seems so.
For general utility cutting, I vastly prefer a drop point to a clip point. I can see the virtue of a clip point for cleaning game and fish, but for general use I find the thin tip of the clip point annoying and frail. With the Opinels, it's pretty easy to file the clip off to a drop point. I did the same with my Case 316-5 and made the knife better to use (for my taste). Of the Bucks I own, I prefer their drop points (Buck 486, Buck 500) much better than their clip points (Buck 110, 112). There is really no general purpose cutting task where I find a clip point better.
For food prep (like cutting a large submarine sandwhich in half), I strongly prefer the thinner profile of the Opinel. I also strongly prefer a knife blade with more belly (like the Opinel) for spreading stuff and like a knife with more length for reaching into a peanut butter (or nutella!) jar.
For heaving cutting, I prefer a locking or fixed blade. When "going after" a tough branch, I tend to twist the blade in my hand a bit. I just feel more confident doing this with a lock or fixed blade. The Opinel #10 is the minimum acceptable for me in this regard. I do trust it, but the handle and blade are both long enough that I could envision being able to bust one if I went really, really nuts. I busted one hammering on it in a vice (they're cheap - I learned some things). I "trust" the Buck 110/112 more in this regard. Obviously, fixed blades are just better in this regard. But... I find I prefer folders over fixed blades. I find folders of this size to be too big to EDC, but they *are* pocketable while working in the yard and such. With a folder, it's super easy to open and close them and then shove them in a pocket (short holster). I *hate* wearing a fixed blade in a sheath. Just hate it. For a truck knife, I wouldn't want to have to undo my belt and thread on a sheath and then unsheath and resheath a knife and walk around with a sheath hanging off of me. Much easier to put a folder back in my pocket. For me, anyway.
My closest use to your "truck knife" need for me is hunting. When I'm hunting, I carry a small pack with some junk in it and I'm not counting ounces. Knives like the Buck 110 are heavy, no way around it. Not a big deal if the knife is riding in my pack when I'm hunting (big issue when backpacking) or when riding in the glove box. The Buck 110/112 is heavy in the hand though too, so that's a consideration. Heavy in the pocket too.
My general back-up knife is the modified Opinel #10 below. I generally carry a small case with a PDA and eye glasses with me most places. The Opinel #10 is so light it slips into that case almost unnoticeably. The blade shape and thinness is much better than the Buck 110 for me and so long as I stay inside of the limits of it's construction, it's a great cutter of anything I've thrown at it.
opinel #10 quarter view by
Pinnah, on Flickr