Fallout 3 Secret 3

When you cross the bridge to the entrance to rivet city, before you enter, chuck a left and jump down onto the platform below. In a large hidey place to the right, there is an ammunition box and a first aid kit. Then if you continue up the steps, it takes you up to the top deck, where a baseball diamond, (complete with bases, bat, and a ball) straight in front of you. When your ready to leave, next to the stairs is the control tower. There might be some other boxes and things on the top of the ship, as i haven't had much time to look.

Fallout 3 Secret 2

It's not much of a secret, but an easily missed item, is the Grognak The Barbarian Comic Book in Jericho's house. It's on the floor next to a cabinet and a poor condition Chinese Officer Sword as shown above.

Fallout 3 Secret 1

If you exit Megaton, and follow the wall until you are at the South side, you will eventually reach 2 - 3 Mole Rats (It's useful to be doing the Mole Rat repellant section of Moira Brown's field guide at this time). Just to the West of them, and a little to the South, you will find a hollow rock. It might be hard to find at first but it has three trees circling it. The rock contains a sniper, some .308 ammo and some other goodies. The location of the rock is shown above.