The bad news is, registration for events at GaryCon V ends tonight. So if you had waited until now to go to GaryCon and game, you'll have to wait until you are actually at the Geneva Ridge Resort to try to get into any games.
The good news is that GaryCon does allow people to purchase badges on site during the convention. Last year the cost for a badge was $10 a day and $40 for the entire run of the convention. And a lot of games that are being run are usually very hospitable towards walk-ups. In fact, I have had instances of having supposedly full games have openings at the last minute. I can tell you right now that though my D&D game is "filled" with six players, I did create eight pregens and can take on two more. The same goes for my HackMaster and Aces & Eights games. Heck, my Aces & Eights game is tailor made for walk-ups. And I am sure that a lot of other GMs will be open to walk-ups as well.
So don't take the deadline passing to hard if you are still interested in attending GaryCon V. There's likely to be something there for you to play if you really want to.
EDIT: Turns out that the badges are $15/day for Thursday or Friday, $25 for Saturday and Sunday or $40 for the entire four days of the convention. Looks like if you can only attend three out of the four days of the con, you're best off getting a four day badge.