I'm seeing two knives already emerging - a multitool of some kind, whether it be a SAK or a Leatherman-style tool, and a strong, reliable fixed blade.
To further refine the inquiry, it appears the multitool should have a saw blade, Phillips head and straight screw drivers, awl, scissors, can opener, and tweezers. I'll add to that list pliers, because a leveraged squeezing tool is incredibly useful.
The fixed blade should first be strong enough to not snap and big enough to function in a wide range of scenarios, but small enough to not be perceived as a burden.
Interestingly, these are the two issued tools in a couple of survival courses I took. The instructors loved the Carbon-V Bushmen for their durability and inexpensive price and preferred Leatherman to Gerber. We were encouraged to bring and practice with any and every tool we wished.
For an everyday compromise scenario, I like to have a Leatherman or SAK with saw and a fixed blade with carbon steel and a blade that's 5"-6" long. Such a blade fits in a backpack or on a belt without being cumbersome or dainty. A Leatherman Supertool 200 or Rebar and anything from a Becker Bk-15/16/17 to a Bark River Gunny, Cold Steel SRK, SWP Rat Ratmandu, or Fallkniven A1 fit the bill for me. I know the Fallkniven is stainless, but I'd be willing, after testing, to take one if I lived somewhere particularly humid.