Grapple hook:
To unlock the grapple hook, take over around three territories after Level 2.
Bald Eagle Persuader boat:
There is a boat called the Bald Eagle Persuader that highly resembles the Gungan submarine in Star Wars: Episode 1. It randomly appears at the mansion near a safehouse in about one out of every ten visits.
Hidden briefing:
Successfully complete the game. Start a new game, but do not save. Instead, load your normal profile to see a briefing on your Extraction list.
Helicopter:
When you get your grapple hook fire it at a passing or attacking helicopter. Then, just reel yourself in.
Agency jeep:
After you kill the man on the boat and finish the mission, you will get the agency jeep.
Taking over sites:
When taking over Guerrilla and Rioja sites, use your heavy drop in your PDA. Choose the truck and just start shooting your way through the entire thing until you have to take the flag at a Guerrilla site or kill the head honcho at a Rioja site.