Play the "Desperately Saving Susan" Nerd Rescue and go to coordinates X: 479.1, Y: 488.3 to find a Xenomorph egg from Alien behind the nerd you are saving. Note: Michael Biehn, who voices the main character, was also a cast member in Aliens.
Dungeons & Dragons reference:
When you need to distract an enemy, you can throw a twenty sided dice at them.
Far Cry 3 reference:
Swim underwater at coordinates X: 531.2, Y: 321.5 to find a scientist next to a toilet, similar to the seasick soldier found in Far Cry 3.
Teenage Mutant Ninja Turtles reference:
During one of the Predator missions, Rex must kill four turtles in the sewers. You can find a pizza box in the sewers and each of the turtles are wearing colored ninja masks.
Easy "Just The Tip" achievement or trophy:
Find an enemy garrison. Disable its barrier inside and try to keep some soldiers still alive. Use cyber hearts to get a Blood Dragon into the base. Allow the remaining soldiers and Blood Dragon to fight each other. While they are fighting each other, get ammunition, health, and other supplies from the garrison's vending machine. After the Blood Dragon has killed all the enemy soldiers, it's health should be knocked down a bit. Use C400 and grenades to whittle down the Blood Dragon's health some more. Use the structures in the garrison to block its beam attack. If needed, get more health from the vending machine. When the the Blood Dragon's health is brought down to just a sliver, switch to the bow. Be patient and wait for the dragon to rear back and fire an arrow into its chest. Repeat the process until its dead.