Avoid everything you see, no matter how small, on a road bike. You'll probably be going too fast to accurately identify it, and it could be sharp. The 1/2" asphalt chunks up here, that are spewed everywhere when there is roadwork going on contain a lot of mica, which shreds tires. So avoid everything you can, but if you get a flat, don't worry: It's a good excuse to take a 10-minute break.