Before The Convention Starts, Sign Up For...
1. A Character Funnel
I have never played a character funnel that I didn't enjoy. I consider these the high point of one-shot play: silly, crazy, wonderful, unique, and condense. These will virtually always be DCC games.
2. A Dungeon Crawl
I made the mistake at Gen Con of playing several dungeon crawls back-to-back, but they were still all enjoyable, and I think one or maybe two of these in a weekend is the sweet spot.
3. A Spooky Game
Most of the time these will be Call of Cthulhu. It's a good idea to have one of these, for variety.
4. Game Run by Honored Guest, Creator, or Person You'd Like to Meet
These are pretty safe bets for some quality content, not least of which because they're games that have been run multiple times for many different audiences.
5. Game in a System You'd Like to Try But Haven't Played
Pretty self-explanatory. No better place to try out a new system than a convention!
6. Someone's Weird Homebrew
These are hard to find, due to usually being devoid of find-able tags, but they tend to be gems in the rough. If someone managed to convince an event coordinator at a convention to showcase their weird homebrew, then they've probably put a lot of effort into it.
And that's it! Six games is plenty for a weekend.