Well, perhaps the 'hammer and a nail' are part of a construction project in Forks. The main character, say Bella, decides to help with building a new community center or something. Along the way, she discovers some secrets about the Cullens or the Quileute tribe because of the people she meets during the construction. Or it could be that the hammer and nail are used in a more symbolic way. For example, a vampire is trying to 'nail down' their humanity with the help of a human friend, using the hammer and nail as a metaphor for holding onto something precious.
One possible plotline could be that a character is using a hammer and a nail to build a shelter in the forest near Forks. This could be a survival - type story where they have to fend off vampires or werewolves while building. Another could be that the hammer and nail are used to repair a special object that has some significance in the Twilight lore, like a charm or a family heirloom.