I generally keep a very sharp , short, serrated safety sheath knife on my belt were I can reach it with either hand in case of my or others' tangling in fishing line, ground tackle or whatever. It's come in handy enough times I don't like to be without it, I have a few more where anyone can grab them quickly.
Short anectodote: Years ago I talked with a hiliner commercial tuna hand-liner who liked to fish solo for giants. I asked him if he ever got tangled in the line and he said, "Yeah, got pulled overboard 5 times over the years, but only had to cut myself loose and swim way back to the surface and up current back to the boat two of those times. I guess I was lucky."