Normally, I always just carry one pannier on the bike. Balance isn't really an issue once you get moving. But today, I had all my clothes, a laptop and an iPad in in one pannier. Add to that pouring rain and wind gusts up to 30mph and that made today's ride a little off balance.
I really had to work and concentrate to keep the bike upright today. Even still, it was fun to ride in the cold, wet rain. It certainly wakes you up!