The most loaded I get is a backpack full of clothes/food and a small saddle bag I carry on almost all rides (tube, levers, quick link, pump, multitool w/ chain tool, patch kit). If I'm carrying extra stuff for cold/wet days it usually fits fine in my jersey/jacket pockets.

I also keep a spare multitool, 2x tubes, gloves, socks, bike shorts, blinkie, water bottle, drawstring backpack, and extra u-lock (as well as my main one) at work. That way if I flat in the morning I'm not obliged to ride home without a spare tube, and if socks/gloves/bike shorts don't dry in time on wet commutes I have spares. Also, if I really need to carry something home and didn't come in with a backpack, I have the spare bag.