Well, is it likely that you could lose your knife?

If your answer is yes: Add a (small) knife.

If it isn't: save the space by using a scalpel blade and then I could add other equipment.

I prefer the last one: I carry a knife on my keychain and a multitool on my belt (secured with pouch and gearkeeper)

It's, once again a personal choice and preference.
I'm respecting your opinion, please respect mine.