You must have a sniper to do the moon easter egg.

You can change the size of the moon by shooting it with a sniper rifle.

For the bridge easter egg, you must have a jet pack to do it beause you have to fly up to one of the Ocean Docks bridges and it will say "THIS IS NOT AN EASTER EGG GO AWAY."

You can get the sniper by putting in the Weapons Set 2 cheat and the jetpack by putting in the Spawn Jetpack cheat (both found on this site).