Just Cause 2 Easter Eggs Hot Air Baloon
Go to X:7392, Y:16151 coordinates. You can ride inside the balloon by shooting off the sandbags. Your direction in the balloon can be controlled by walking in the basket. You can also find an armor piece near the balloon.
Lost Easter Eggs
X:1743, Y:4363 coordinates
Got to the coordinates X:1743, Y:4363 to find the hatch from the TV show Lost. There's also a smoke monster on the island who can be heard occasionally, though he sometimes appears around X:2275 Y:1681.
Hidden Race Track
Coordinates will take you to a small island full of fast cars and closed, winding roads for racing.
Billboard Easter Egg
Baby Panay Billboard
Look for any billboard with the dictator Baby Panay on it, use your grappling hook so that Rico is positioned directly over his face and press the action button. Rico will draw glasses and a mustache onto the billboard.
Happy Bubble Blaster
X: 4245 Y: 25978
At these coordinates you'll find a tower in the middle of some cherry blossom trees. Use your grappling hook to get up into the tower and you'll find the Happy Bubble Blaster weapon on the table. You can equip it and spray bubbles on your enemies! Note that it doesn't do any damage but will still provoke the guards.
Shark Easter Egg
Swimming around the water near X-12665 Y-22595 you'll find a large shark fin patroling the area. Closer examination will reveal it's just a little motor with a big metal fin.
I Am Legend Easter Egg
X: 18207 Y:21543
At coordinates X: 18207 Y:21543 there are a table and chair on a doc, a reference to the scene in the film where Will Smith is looking for any survivors.
Whale Easter Egg
At the bottom right of the map on the Selatan Archipelago near X:29601 Y:31301 there is an enormous beached whale on the shore. Blowing the whale up with the timed explosive will reveal an armor part in the belly of the whale.
This is most likely a reference to the classic news video of a beached whale being blown up with explosives.