I vote NOT for the watch. Old watches are mechanical nightmares that in many cases aren't even very good at their only function. Watches used to be prized because they were relatively expensive due to all the labor required to make a decent one. Almost any modern watch outclasses every older one except maybe in ornamentation and sentiment. I know some people are really into expensive watches, and that's fine with me, but I totally don't get it.
Guns are still just as good as when they were made, but I can't really carry Grandpa's 12 gauge around with me most places.
Knives, on the other hand, can fit into your pocket and do just as good a job as cutting tools as ones you can buy today. The only sentimental objects from departed family members I routinely have on my person are pocket knives---so I vote for them.