Hey I just recently got a Fixed gear bike and am enjoying it a fair amount.
I'm supposed to do a 68 mile chairty ride at the end of the summer and have decided I want to do this on my fixed gear.

Any tips and or suggestions?

go out there, have fun. did a century on my fixed gear, it was awesome.

Ride the area where the ride is supposed to take place, if you can, to make sure your gearing is right.
Spend time on the bike. Your butt will get sore before your legs get tired if you have not spent enough time in the saddle.
Drink water every 10min, eat (light) at all the rest stops.

Sign up for a century.

Enjoy

Just put in some miles. If you can get to the point you can do a 30 mile ride easily 68 will be no problem. And figure out what your nutrition/hydration. As powers2b said, its very helpful to keep a continual flow of food and water into your system. There are some foods and sports drinks I can stomach on long rides and there are some that I can't. For instance, the HEED sports drink mix I simply can't get down, the same for gels, but Gatorade G2 and Clif Shots bars I find great. It's all about personal taste.

My $.02

Just ride.

Don't get black out drunk the night before the charity ride, as you may forget to set your alarm and miss it.

Bring some water and eat some food, you'll be fine.

I'd suggest a pair of handlebars with multiple usable hand positions, for when your hands start to go numb at mile 30. Water bottle holders as well, one or two. And a brake, for when that idiot commuter on their hybrid swerves in front of you.

Your ride lacks three qualities that make a brevet a brevet. First, it does not have time controls, second it is not long enough (the minimum is 200km) and third it is supported. While I appreciate you feeling the need to prepare for a 68 mile ride, as it is likely your longest to date, you are not riding a brevet.

agreed. It'll be a fun ride tho

I've done at least 3 100k rides, this season, on my pista. Just ride 30 to 40 mile rides a couple of times. If you're riding a track geometry bike, you're going to feel it on your hands, wear gloves. If your bike doesn't have places for water bottles get a camel back. In Dallas every rally vie done it's been over 100 degrees. It's incredibly insane how much water my body goes through. Also. And this is the most important factor, pace yourself. It's really easy to get carried away in the beginning of the ride especially when there are all those people riding around you.

Also one big thing is, at the rest stops i had tons of people stopping and staring at my rig. Question after question. I even had people taking pics of my girl. It was odd. Some of the off hand comments while riding from the road bike people got on my nerves after a while.

Other than that. Enjoy yourself. I love riding my fixed gear. At the end of the ride. It's just a long ride vs the shorter rides you do all year. If you enjoy yourself, which I do, then you won't get tired as quickly..,,

Socks