I'm taking the literal meaning of the question on this one, 1 knife for everything.
A J. A. Henkels 8" Chef's knife, good high carbon steel, full tang, 3 rivet construction, German engineered and made.
I'm thinking that no matter the situation, we're going to be eating much more often than fighting. The 8" chef may not be the quintessential fighting knife, but it is the benchmark in the kitchen.
Oh, BTW, I wouldn't feel "under-knifed" with a good 8" chef in my hand in a fight.
"Your fear is 100% dependent on you for it's survival." - Steve Maraboli, Life, the Truth, and Being Free