Finish Just Cause, then start a new game. Don't save then load your normal Profile. You should have a briefing on your Extraction list. It will get you to the first beach in the game.
Agency jeep
After you kill the man on the boat and finish the mission, you will get the agency jeep.
Bald Eagle Persuader boat
There is a boat that looks oddly like the Gungan submarine in Star Wars Episode 1. It is called the Bald Eagle Persuader. It travels ridiculously fast on water. If you drive it in a straight line for long enough it takes off and wings grow from the side. When you land it, wheels pop out underneath. It is very difficult to control. It appears about one in every ten visits to the mansion near a safehouse. It cycles in this order: sea, air, land. If you go from the air to the sea it will just explode.
Boarding the President's plane
When you are flying the jet in the final level, fly over the top of the plane. Try to hover over one of the wings or the front of the plane (recommended). Quickly jump out of the jet and let go. If done correctly, a "Jump to vehicle" icon will appear. Quickly press A and he will grab on and you will immediately appear in the plane.
Grapple hook
After Level 2 there are territories you can take over. Once you have done about three of them you will get the grapple hook.
Helicopter
When you get your grapple hook fire it at a passing or attacking helicopter. Then, just reel your self in.
Taking over sites
Use the following trick when you are taking over a village with the guerrillas. Ignore most of the enemies and charge towards the roadblock the government has up. Destroy it using grenades, a rocket launcher, or timed explosives. Do this to each one, and the "Capture enemy flag" objective will soon appear. Run to it and press A to conquer that area. For other villages without roadblocks, such as the towns when a police car with a turret on the back appears, go in it. One of your teammates will also enter. Drive down street and your partner will kill everyone. Then, capture the flag when instructed. Do not open fire on anyone on your team or they will kill you.
After Game "Briefing"...