This is the 3rd quest you receive from Donald Love and is a part of the main story line so it is unmissable. Donald tells you there will be a plane dropping packages in the ocean shortly and he wants you to pick them up before anyone else does.
When the mission starts there are 2 blips on your radar, a purple one for a boat and a yellow one for the plane. Ignore both blips. The yellow blip for the plane is irrelevant. The purple blip for the boat takes entirely too long to get too because its back in Portland and has no easy path to get to it. You only have 2 min before the plane starts dropping and not much time after that to pick them up.
Sooooo... instead head to Asuka's place. There is a dock right next to it and there are always boats there. You can take any boat to do this mission. A faster one is preferable but any boat will work. Get a boat and drive directly under the Callahan bridge.
You should be close to the plane (yellow marker) now and should be able to see it soon. Position yourself so that you will be just behind the plane and wait for the 1st package to drop. Once its in the water get it and follow the plane picking up packages as you go. There are 6 in total and your wanted level increases by one every time you pick one up. Once you have the 6th package head directly back to the dock at Asuka's.
Once you are on land again run up the stairs and get in a car. Preferably a fast one such as the Yakuza one that's always there. Now you have two choices in how to deal with your 6 star wanted level. You can either drive to the Pay n Spray a short distance away and clear it or drive to the objective which will finish the mission and clear it. Both ways work but going directly to the objective is longer and slightly more difficult because a 6 star can be a pain. Once you enter the blue circle and the mission completes the trophy will unlock.