The Second Amendment does apply to knives. Know the knife laws in your state, and in other states you may find yourself in.
If personal protection is a priority for you, a knife is something that you can use right away, without having to identify yourself or register the weapon.
I’m glad to see people talking about options. Not every tool is going to suit every person’s needs or wants.
I also have a nice camping knife with a ferro rod. I can process wood and start a fire. I can clean game and fish. It’s big enough that it could put someone off getting too close, but yes, I would have to be committed to drawing a lot of blood.