Well, when I was in security I carried a KA BAR TDI behind my mag pouches that was specifically for weapon retention. Never for anything else.
I'm in the not big on a dedicated combat knife for SHTF. I carry a few knives EDC and each have their uses. When I was in the Army I had a basic pocket knife and at one point either a folding locker or a fixed blade on my LBE. Later I carried a SAK Champ in a belt sheath and a fixed blade on the LBE.
There is a reason many of the field type knives have sheaths with the little sharpening stone in a front pocket on it. Keep your knives sharpened in the field. A good, fixed blade field knife that is kept sharp will handle tasks from cutting 550 cord, cutting sticks, and cutting flesh.
You will have limited space and weight on your gear. Especially in SHTF. So use the valuable real estate and weight to carry a quality field knife that you can sharpen in the field without having to take a bulky sharpening system along with you.
The issue with having a dedicated fighting knife on your SHTF gear is the same as a lot of the stuff people put on their gear, only more so. They haven't trained and practiced with it. Pulling a knife as a last ditch, try to save me butt because everything else just went south is one thing. Knife fighting and really running a knife as a full on combat implement means you better be putting in hours, weeks, months, and years, of getting real instruction and doing real practice. Then actually practicing drawing that blade from your gear, while wearing your gear, and sparring in full kit and in realistic simulations. Otherwise, use the real estate or something you can and will use to survive.
Btw, my best friend at Ft Bragg had been nine years in SF back in the late 60s and early 70s. The most I got out of him regarding those years was that he was in Thailand, that the reason they wore gold link chains was they could break off links in the boonies and use them as currency, and he carried a Randall Model 14 knife that he used for all kinds of things.
When he came back in the Army after 9 years out, when I met him, he still carried that same Randall Model 14 knife. He carried it during mountain training at Ft. Greely, AK, when he was part of the 82ND restarting LRSD, and later as a Ranger Instructor after he left Ft. Bragg. (He also went through Ranger School back when you had to be in the top two thirds of the class to wear the tab.)
So this fellow who was both SF (with substantial experience) and Ranger tabbed carried a fairly heavy knife, but one that he got the most and varied use out of in a variety of combat operations and situations. I'll take his example as an answer to the question. I have a Randall Model 14 because a person I really respected and admired thought it was a hell of a knife to carry in real world situations.