The rules are easy and will be familiar to d20 players.

Anyone can volunteer to be a pinch DM, but they have to be prepared. Usually 2-3 of us are at any given moment.

The rules are kinda odd, but the world is absolutely perfect one-shot material.

In the time before all players show up, we usually just chill and watch movies…thanks to my movie collection that grows almost weekly…

I’d actually recommend having everyone in the group create a character (including the GM, and it really takes about five minutes) when there’s nothing better going on, and save them for the next time a backup is needed. When you need to pull out the backup, whomever has an interesting idea gets to be the GM. Or, if you really want to be wacky, run the characters through the exact same adventure you were planning for the full group. The look on the player’s faces will be priceless.

I was just running a game last night (designed to be about a 4-5 hour game, run across a 3 hour session and a follow-up), and everyone had a great time. The game has a very palpable feel of desperation that makes the games fast. The dice mechanics are easy, and with the right group the game can actually be moving in an odd sort of way.

One suggestion that my players had that would likely work for a pre-gen game would be ‘My Life With Vader’ (or ‘My Life With Palpatine’) having the players take on the role of Sith Apprentices. In fact, the entire Star Wars saga could be framed as Vader playing ‘My Life With Palpatine.’

Some other games that work well for one shot games: Dogs in the Vinyard, Poison’d, Contender. All have simple mechanics that can get a bit tiresome after a while, but make some very memorable sessions.

We tend to play boardgames when someone goes missing, though on Friday our canceled session led us to hit Iron Man at the theater instead.

Spirit of the Century seems like an ideal “go to” game– generate characters one night (when everyone’s there, most likely), then run one shot pulp adventures with whatever people show. It works well for con-like settings, though I think people would enjoy getting to play the same characters again. Playing it as a backup game would fulfill that desire.

http://www.evilhat.com/home/?page_id=103

Spirit of the Century was pretty much built for this problem. The GM looks at the aspects of whoever is playing that night and builds something tailored in 10-15 minutes. It does require taking a session and making characters but then you get to mine those characters for one shot gold for many sessions without much in the way of heavy prep.

http://www.dog-eared-designs.com/games.html

Another game I’ve heard to come to with nothing more than a blank sheet of paper that is capable of making gold is Prime Time Adventures, sadly I haven’t had the chance to personally test it yet.

I also like the old standbys, like Settler’s of Cataan.

There are a few ‘one sheets’ published for it, and any GM worth his salt can come up with more on the fly.

Yarr!