After Level 2 there are territories you can take over. Once you have done about three of them you will get the grapple hook.
There is a boat that looks a lot like the Gungan submarine in Star Wars: Episode 1; it is called the Bald Eagle Persuader. It travels very 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. Note: It cycles in the following order: sea, air, land. If you go from the air to the sea it will just explode.
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.
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.