Secured the weapon the transport truck was carrying
One of the hidden objectives is connected with securing the cargo. It is good to complete it when playing the mission for the first time, because you can obtain a perfect weapon for destroying APCs and tanks. Wait until you're informed about a truck with valuable cargo. It will start from north of Yakho Oboo Supply Outpost and will be heading south. Stand in any place on the truck's route and block the way (you can even use a simple Cardboard Box).
When the truck stops, knock out or kill the driver that should get out of the vehicle. If you have CARGO 2 upgrade, you can Fulton the whole truck. However, a better idea is to get on top of it and collecting the CGM 25 rocket launcher. This weapon is perfect for destroying enemy vehicles - you just need to wait until it locks the target and shoot a burst of missiles.
Extracting APCs and tanks
There are two hidden objectives connected to extracting enemy machines. The first one is to Fulton any APC (out of seven that you can find on the map) and the second one is to extract all three tanks that appear on the map later in the mission. In both cases, you will need CARGO 2 upgrade. It is available only after completing mission 10, because one of the requirements is to have a Transportation Specialist, who you will find in that mission. Before you Fulton a given machine, you should stop it. In the case of APCs, a simple Cardboard Box will do. However, to stop a tank, you will need a bigger obstacle, like for example a jeep. Be very careful every time you want to extract a machine and don't let yourself be seen.