Vault 3.14/0: Serious Sam, Duke Nukem, Chuck Norris, 50000 pissed off aliens and a fully stocked armory.
Vault 666: 500 satanists psychopaths, lots of bits and pieces of machinery, and the Saw movies.
Vault 321205: 200 catgirls, 200 catboys, pink vault suits, all entertainment is romantic comedy and cartoons, and food dispensors permenatly set to 'sweets'
Just for referece, those are 3.14 divided by zero, the number of the beast, and 3 21 20 5 referecing letters of the alphabet. I'll let you figure out what it spells. Also, you didn't say it had to be realistic or fit into Fallout lore so if you got any problems with my answers, please direct them to that brick wall over there.