A Vampire Slayer's Kit contains four Masterwork Wooden Stakes. They are listed as a very weak weapon, just a bit weaker than a dagger. Being Masterwork helps to hit with them just slightly more often, but that's it.
They cannot be used to impale a vampire until the creature is already helpless, unless Called Shots are allowed, and even then, a critical hit must be scored. I would not attempt a tactic whose chance of success is less than 5% (because a critical hit also needs to be confirmed). Well, this would work for somebody who can reliably deal 50 points of damage with a wooden stake, but this would be a weird situation, especially given that the stake is a light weapon: you only add half your STR bonus to strikes.
I then thought that it could work as a Masterwork Tool for slaying a helpless vampire, but this is not World of Darkness, and no check is required.
Now, this seemingly worthless item costs 300 gp because it is Masterwork. You get it for "free" with the kit, but I might just be missing something.
It could be used in breaking the game via buying the kit for 500 gp and then selling the stakes for 600 gp, but Golarion's economy is weak enough and doesn't need another punch.
Is a Masterwork Wooden Stake actually worth anything other than fluff?