I just carry my waist pouch, it's very flat and small. In it has the crankbrothers mini tool 10, ipod, key, money (I don't carry my wallet while riding), identity card, small bit of tar. There's plenty of mcdonald's and 7-11 for drinks and food at my side.
I haven't heard of any riders at my side carrying so many spares! Tubes and patch kit at the most. If anything breaks, like the crossover or bb, we would just take a taxi home.