Whooo! What a fun thread.
I was going to propose epoxy, cordage, wire, or tape (as others did) but this discussion was way more fun. I like the swiss cheese on Mt. Everest comment the best, that's very zen. What sound does the swiss cheese on Mt Everest make? Think about THAT.
So, a lot of us walk around with a way to cut at all times. Makes me wonder why we don't walk around with ways to join, at all times. But who carries epoxy in their pocket or in a sheath on their belt?
But a knife whose handle is wrapped in duct tape, wire, or paracord is, in a way, the complete environmental-modification package: separator and joiner all in one.
If I were in a survival situation, or any expedient "modify the environment" situation, I think I'd want epoxy, cordage, wire and/or tape right up there with a knife and a flint.