Interesting ideas so far. I had an idea myself, and like a few others, tried to think of something that didn't depend on a McGuffin or anything with a Vault.
But, a Vault could easily play a role, albeit just in ancestry (like the Chosen One's distant relations to Vault 13.)
You're essentially a tribal part of a formerly primitive outpost. Your Vault was destroyed/raided some time ago. Maybe a generation or more before the games beginning. What could have been a Vault City lookalike, instead got annihilated early on by this mysterious force. They stole most of the Vaults easy-to-carry technology, and took many of the skilled people as slaves. Imagine how much a scientist would fetch on a black market? Need a new drug? Buy someone to create one. Want to start an army? Buy an engineer. Anyway...
The Vault was almost gutted to uselessness, as was many of the people. Now, a Vault obviously would have armaments, so not all was lost. Survivors stuck to their guns, and beat back the more seasoned forces. Very mercenary-like, once the going got tough, they pulled out and just cut their losses. The few soldiers they lost were great investments for the many pricey weapons, tech, and people they make off with.
Now, back to the beginning of the actual game. After the disastrous history, the Vault would still be a reservoir of useful things. It won't be a Vault City, but at least they could survive. Maybe they have their own water-source still thanks to the depth of the Vault and some of the inner-workings. Cannibalizing the entire Vault for electronics, they start a new town above-ground. With the water being pumped, they manage to survive and almost thrive. The 'hero' could have any number of reasons for leaving.
--As someone mentioned, they would like a good/evil/neutral/snarky divergence early on, and I do agree to a point. EVEN if its not binding to the end of the game. Imagine being cast out of the town at the start of the game for being a punk, stealing, or even murdering a friend or maybe even your parents. You start the game off harder, (and you might or might not get a Pipboy right away. Stealing yours, paying a hack-doctor to graft it to you might be what gets you kicked out. And if you go the good-route, then it is a reward for maybe saving someone during a raid early on. OR, even better, its part of a dowry. Think I spelled that right, anyway, its a gift before a marriage, and maybe you have to go prove yourself in the world before they fully let you have your betrothed. Whether or not you actually Want the chick. Or.. a man. Maybe thats why you run away.
)
Woo, back on track. *Rubbing his chin.* Ah, yes. After getting a Pipboy then, or soon after, you head out into the world, determined to get revenge on your town, help it by trying to find trade with a neighboring town (doesn't have to be Las Vegas at the start. Vegas could very well be the 3-6th town down the line you get to).
Down the line, you could maybe join and then take over a Raider group, and even return to destroy and then enslave your former community. The raiders may have been on the run and needed a new headquarters, and by handing your former town to them on a silver platter, per se, you also have earned your right to lead them. The place will still exist, but in a very dark way, with your former family and friends under collar and butchered. Then again, maybe you start to join the raiders, hoping to make something for yourself, and when you find out that maybe they are heading for your community, you decide to save them. This can be done even if you were evil at the start, this will be your redemption. You lead them there, then backstab them at the assault, and slaughter the Raiders.
With adulation and applause, they accept you back to their hearts. Which, you might still turn evil again later in the game, just for an even Bigger plan than a simple raiders HQ. By gaining their trust, you might politic and take over your home. Turning it into a haven of maybe farmers, or soldiers (which you need to arm by buying trade and opening up to Vegas), you become a new power in the local area. With time, you invest into Vegas, becoming a new crime family. Now, you might have to silence some of your people who protest, but others will embrace this new life, seeing it as a way out of their meager existence.
... I got off track. But, there is alot more I could go into.
Back to what I should continue saying, Ahem.
No matter how you slice it, you pass through Vegas early on for one reason or another. (maybe seeking a black market doctor to put the Pipboy on your own that you stole/killed for. Not being able to pay for it, you might owe him a favor and then become indebted to a crime family, who owns the doctor as well.)
Maybe by opening up trade from there to your home, you also expose them the former people who almost destroyed your past generatoin. Finding out that there is still people, in time, you return home to find that it is mostly burning and destroyed. (This could be rebuilt, left to die out while you move yourself to Vegas, or among other things is up to the player, of course.) You find that there is a market dealing in technology in Vegas, which is almost solely fueled by some force that steals it from the nearby states and lands. Vaults being an easy target if one knows where to look, it could be quite profitable, especially for a small mobile task force. Small amount of people = huge rewards. Put a few in power armor to act as tanks for primitive weaponry/low quality guns, bam, few losses, total win.
You might go so far as to specifically taking over a crime family JUST to either join/destroy this Mysterious Force. Or... dare I say it, take them over. You might just later own All of Vegas (probably quite hard and maybe not even lasting.) But you use that power and resources, and then absorb the Force. A part could resist, hiding in a military base far to the north (south, east, whatever) that you must snuff out. That could be the end-game, no matter what you did. The leader could be there, or the leaders liuetenant (incase you actually convinced the leader to join your cause for whatever reason). Depending how you do it and played the game, the last base could be quite large, or smaller than expected. If you made things difficult for them, they won't have as many men to deal with. Or maybe they'll have back-ups of ghouls or mutants if you managed ot make enemies of certain towns outside of Vegas because of your methods.
Remember kiddies, evil plays the enemy of my enemy is my friend game too.
In the end, depending how you want to evolve, you might change from good, to evil, redemption, vile throughout the whole story. Maybe your character is actually a bit insane, and some of this was done just for a lark. Imagine at the end, instead of turning everything into a empire, utopia, crime syndicate, corporation....
You instead release the dogs of war, assassinate every leader that followed you, and then disappears into the wastes. The endings could be quite interesting to see of what happens to your legacy when you re-introduce anarchy to all/none/partial of the entire state of Nevada.
Wow. I wrote a lot. From the top of my head. I hope someone enjoys reading this at least. I spent about 20 minutes writing this.
especially the Vault Dweller.
