Most, if not all of us have done the survivalist RP in Fallout 3, but have you tried a pure downtown DC character? Here are the rules...

Play on hard or above.

Turn the HUD off

Turn music off

No fast travel

Once you leave the vault head straight to DC ruins and spent the entirity of that character in the DC ruins.

That means not once leaving the ruins to visit megaton... your only merchants will be in underworld museum... but seldom will you stumble across the mall if you're not intentionally heading there.