I was interested in hollow handle knives when I saw
First Blood as a kid . . . but the cheaply made hollow handle knife that I bought broke when I tried to use it on a backpacking trip.
So I was put off such knives until I discovered the Schrade SCHF2, which is made from a single piece of metal.
I had a custom leatherworker make me a bushcraft sheath for it that has a side loop for a ferroceramic fire rod.
As an exercise, I tried to see how I could trick out this arrangement to see if it's actually practical.
I managed to use a minature Zippo-type lighter with a rubber seal (so the fluid doesn't evaporate), fish hooks, fishline, sinkers, a tiny keychain-style multitool, dental floss (for sewing), needles, a wire saw, a tiny keychain-style flashlight, extra paracord on the outside wrapped around the firesteel loop, and a few other things.
I experimented with this setup in the woods behind my house, and everything seemed to do what it was supposed to do.
Hopefully, I'll never be so desperate as to rely on the contents of a hollow handle knife to stay alive.