I've gotten to where I haul in a weeks worth of scrubs and underclothes one day a week, which all fits in one Ortlieb pannier. Lunch and phone, wallet, keys, glasses case, tools, pump, spare tube, etc, all ride in my big saddlebag (18L Zimbale) on a Carradice quick release bag support. The saddlebag I carry everyday. If it is going to be windy I'll skip using the Ortlieb and just cram one days worth of clothes at a time into the saddlebag along with everything else, which often means taking advantage of the "long flap" feature.

I'm very lucky in that the bicycle commuters locker room at work is an old locker room for the OR's that is no longer used except by a few doctors and a handful of cyclists. Out of something like 100 lockers, at least a third of them are empty so I snagged a couple for stowing work shoes and clothes.

I am back in college again, last quarter my class was online so didn't impact my commuting at all, but now I've got a book bag strapped to the top of my front rack most days as well. I'll have to snap a pic. I wanted the smallest possible bag that was able to hold my book, binder, lab logbook, calculator, and paper notebook. Turned out I had a perfectly sized rubberized military surplus satchel amongst that kind of thing that I tend to collect. I bungee this to top of the rack, which is more handy off the bike than any of my panniers, and centers the load, instead of having all that weight hanging off of one side. I'm used to riding with a fair amount of weight on one side of the front wheel, but don't like to do it every day*.

* I leave the book bag at work Friday night, carry the dirty clothes home Saturday morning, bring the clean clothes in Saturday night, and take my books back home Sunday morning. The bike I use for commuting doesn't have a good way to attach a rear rack, so I've just got a front rack and the saddlebag on it.