Just one. You ARE kidding, right? OK, I would select a Bowie or large camp knife, with a blade in the 7" to 9" range. There are several candidates, and if I had to select from among what I presently own, it would be a Randall #1-7, with a micarta handle.
I would prefer something with full-tang construction, for a one-and-only knife, that might see heavy, abusive use in an emergency. Having an axe/hatchet and prying tool handy would minimize the need to abuse the knife.
In my usually-urban life, I have little need for a large knife, but plenty of use for smaller
blades, so I am glad I am able to own a variety of knives! SAK, small and large folders, and small fixed blades see varying amounts of regular use. Neither of my Randall 1-7 knives have to work for a living, at this point in time.