Shortly after you return to the ranger camp and you trigger the event to leave to the main area, the keys jump into your inventory :)***SPOILER ALERT***There's a short comedy scene where Ed loots the dead guy's body and Marcus and Maya snap at him for it. He steals a radio and the keys :P These keys can then be used inthe truck :)
It's possible to jump the bridge with the truck. Just have to gun it and make sure to hit the bridge straight on.
You are not allowed to request a sticky.