The Forsaken

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Sean (Kerr Smith) is driving cross country to his sister's wedding when he picks up Nick (Brendan Fehr), a hitchhiker who happens to be a vampire hunter hunting a group of vampires led by Kit (Johnathon Schaech), one of the Forsaken.
The Forsaken are a group of French Knights that during the First Crusade made a pact with the demon Abaddon to live forever. There were nine knights: eight were turned into vampires and became known as the Forsaken; the ninth was a sacrifice to Abaddon to seal the pact. Of the eight, four are dead, one is in Europe, one in Africa and two in the United States (including the one Nick is tracking, Kit). Nick was bitten by a vampire but, thanks to an antiviral drug cocktail, the vampire virus is kept at bay. Each of the Forsaken carry a unique strain of the virus and killing the Forsaken kills the entire strain of virus; killing all the vampires descended from it, and stopping anyone just infected from turning, which is why Nick is hunting this particular Forsaken. He believes him to be the one that his strain of the vampire virus is descended from and that if he kills him, he will not eventually turn into a vampire (as the drug cocktail eventually will lose effect). At first Sean is less than willing to indulge his new acquaintance, but then they find Megan (Izabella Miko), a girl Sean finds he is attracted to, bitten and left for dead by the vampires. Nick also proves he is telling the truth by killing a vampire, Teddy (Alexis Thorpe), by exposure to sunlight.
When Sean is infected with the vampire virus (Megan bites his hand while he's covering her mouth), their only hope is to kill the vampire leader before it is too late. The Forsaken must be slain on hallowed ground, so the three head for a Spanish mission 60 miles away â chased by the vampires and their day driver Penn (Simon Rex). After a battle on the road Penn is killed and the car is running out of gas as its tank was shot so they are unable to reach the mission. They stop at a gas station where an old woman named Ina (Carrie Snodgress) lets them in after seeing Megan. She shows them a newspaper connecting Megan to a bloodbath in Arizona; when Megan wakes up and is coherent enough to talk, she explains she was a victim of the vampires' bloodbath (led by Kit) and after Kit bit her he left Teddy to kill her, which she did not do for some reason. Kit and Cym (Phina Oruche) then catch up to them and lay siege to the gas station.
Sean discovers a graveyard outside and Ina explains that it is an old Spanish graveyard that was never dug up, making the house hallowed ground and thus a suitable place to kill Kit. In the following battle, Sean blows up Cym's head with Ina's shotgun but both he and Nick are injured and Kit forces him to be his new day driver then goes after Ina and Megan. As Kit is about to kill them Sean drives his car through the gas station wall and pins Kit to the wall, hoping to hold him there until the sun rises. Kit pushes the car back when it runs out of gas due to the hole in the tank but Sean then shoots him, knocking him into a beam of sunlight and shoots him again when he manages to escape the light. As Kit starts to combust, Sean, Nick, Megan and Ina flee the gas station; Kit's explosive death ignites the gas. It seems Sean and Megan are finally clear of the vampire virus, however, Nick is not cured as it turns out that the vampire responsible for his infection is descended from the other member of the Forsaken in the United States.
Nick takes to the road to try to find and kill the other Forsaken, leaving a letter of thanks for Sean. Three months later, Sean catches up to him driving Kit's car and insists on helping, having discovered that the Forsaken is probably in Denver. The two set off for Denver.

Question: What does Nick leave for Sean?
Answer: a letter of thanks