Limited Edition Halo 4 Copy
As soon as you wake up on Dawn, look around the Cryo room and you should see two or three Halo 4 Limited Edition Copies on the floor.
There are a also a few more scattered copies around the map like on the ramp where you can assassinate the Elite on the ramp control center shown in the video below.
Master Chief's Service Record
After exiting the pod at the start of the mission Dawn, you'll head down a hallway with a yellow hologram visible in the room at the far end. If you look to the left as you move towards it, you'll find some stairs heading down. If you follow them tot he bottom you can find a terminal that will give you a brief overview of master chief's exploits to date. this is covered in the above walkthrough and by checking it out, you will also earn the achievement 'Digging up the Past'.
If you have any more Halo 4 Easter Eggs, then post it!