I don't have a bag, but I hope a backpack counts. I stopped carrying bags many years ago after I read about how a bag gets your body off balance. Even a set of keys in your pocket is harmful. So I have a sensible canvas black backpack that goes with everything. My only requirement is that an A4 folder can be fit into it. In the main compartment I have my diary, books (for some reason, I always carry books to and from work and between buildings at work) and my wallet. In the inner pocket I have my mobile phone – always switched off! - compact powder, lipstick, comb, USB stick and a field pharmacy. In the outer pocket, I have my keys, university card, a fancy Oriental business card holder (a present of course) and an assortment of pens. I am horrible with pens. No idea giving me an expensive Parker, I'll lose it just as easy as a promotion ballpoint. I am very careful about putting everything in the right compartment because if I don't I'll never find it. Every now and then I panic because I cannot find my keys or my card. Almost every time I have put it in the wrong place.
Tonight I went to Formal Hall, and I don't want to carry more than absolutely necessary with me. Fortunately, I can put my car key into the sleeve of my gown!