One of the things I miss about working in an office is finding a group of folks to play games with at lunch. I'd often play short games like Carcasonne, Munckin, Rheinlander, Three-Dragon-Ante, and Gloom. But we'd also play RPGs, namely Simple Superheroes.
I found these lunch games to be extremely invigorating. It takes your mind completely off work, let's you relax, and get back to work sharper and more alert.
The classic RPG "timeslot" is 4 hours, so playing over lunch has a few challenges, but it is very satisfying. Rules light games that play fast, like Simple Superheroes, work surprisingly well over a lunch break. I have some fond memories of playing a bit of AD&D at lunch in middle school, but my more recent memories trump those.
Here's a few advantages of lunch games:
1. Focus: The shorter time period means that you and all the players will be focussed. You'll be surprised how much gameplay and story you can cover.
2. Serialized Storytelling: Superheroes lend themselves very well to serialized story-telling. Keep things straightforward to start, and layer in complication as needed. This time frame really suits what can be covered in an single issue.
3. Low Prep: Because the games are shorter, as GM you need to do less preparation. It also tends to leave you a little more relaxed, and you can respond directly to what the players seem interested in. This also gives you some space to come up with interesting twists that you might not otherwise think of.
4. Explore those Characters: Players seem able to direct the story more. Some of this is due to the '3 low prep' mentioned above (coupled with GM willingness to customize the story to the characters) and '1 focus.' Players come to the table wanting to contribute to the story, and its in more manageable chunks.
Here's a few things to keep in mind when running games over lunch (or over a short period of time):
1. Eating and Socializing - set thing up as people start eating and socializing. Give everyone at least 5 minutes. Starting things off with some Roleplaying tends to let those slower eaters catch up.
2. Punchy Plots - simple names and plots keep things easy for everyone to remember in an ongoing campaign. You can layer in complication if needed, but never underestimate the power of classic stories with a twist of your own characters.
3. Cue Card Character sheets - sometimes you won't have room at the table for people food, dice, GM notes and full sized (8x12) character sheets. Cue Card sheets take up less space, and also seem to focus people in on the story more.
4. Plan 2 - 4 events: a couple fights and a couple roleplaying events are usually (more than) enough to keep the table busy. Simple challenges can also be good additions.