Start the game with the "restart +1" command line parameter.
This trick works best on the Flaming Dart level. Get in a jet and fly straight up until you cannot go any higher. Then, bail out. Everything should be white when you bail. When falling, your character will scream. A few seconds after the screams stop, you can hear him crapping his pants.
The Chinook can float on water.
To fit more people than the maximum amount in a Chinook, jump into the back opened hatch and run towards the front of the chopper. If you use the parachute in it, the game will automatically put you outside floating down. This works well when you have a short supply of transport vehicles for a good ambush. The same thing works for a boat. You can fit many people in it.
Napalm will burn straight and backwards. This will help when hitting targets. Also, if you get hit by napalm do not move and you will not burn.
You need to be a C4 engineer for this trick. Find a jeep and weaken it about 80%. Plant C4 charges on the hood. Get in it and hit a car, tank, or anything else. The C4s will detonate, and destroy what you hit. Note: You can jump out of the jeep just before you hit the target, but it may not explode at the first moment.