I have a Topeak MTX trunk bag, I use it on my 50+ mile ride on Saturdays, I also have the fitted rain cover that works really well. Since it rains almost every day, I pack flip flops, dry socks, shorts, shirt, underwear, towels, and contact eye solution. If I get stuck in a downpour I find a dry place that serves beer, change into dry clothes and flip flops, and try the best I can to dry out my shoes. I have had to use this set up about 50% of the time this summer.