Drinking more before you start out will only delay the inevitable if you aren't regularly taking a few gulps from your bottle while on the bike. Especially those long rides.

Learn to grab your bottle every 10 - 15 minutes and take a few gulps. Riding in groups it can be a little unnerving to pull a bottle out. But once your other friends see you can do it safely, they won't be so unnerved about the possibility of you causing them to crash. <grin>