I leave my shoes at work, in my desk, so I don't have to carry them everyday. I have a small-ish seat bag (recumbent) that I use about half the year. I'll be ordering a bit larger bag in about a month for winter gear. It'll be cold enough that I need my winter gear in the mornings, but not for the ride home, so I'll need a bit more space than I have now. You might also think about what else you can leave at work that you don't have to carry back and forth every day (deodorant, snacks). I try to take most of my food in one or two days and leave in the fridge at work, also.