It really depends on what bike I'm on, and what my mission for the day is.
For my daily work commute, two Ortlieb pannier (backroller classics), unless I get a wild hair and ride my fixed bike, then an ancient XXL Timbuk2 messenger (which had carried everything from work clothes and my lunch, to a Stihl 30" chain saw with bar oil and a small can of premix, to Mungo -- my friend's 8-year old child -- he loved it). I also use the messenger if I'm going to be locking up in a sketch place -- much easier to carry around with me, and my 'beater bike' doesn't have a rack anyway.
If I'm just headed to town for breakfast and a ride up our coastal trail -- worth checking out if you find yourself in Anchorage -- a medium Jannd messenger has been my go to, but it was recently replaced with a Patagonia Black Hole messenger (jury is still out on this one, but the Jannd kept breaking buckles.
In the past, I've also regularly cycled with my ski pack (a Backcountry Access), complete with skis, poles, and everything I needed to patrol for the day while wearing plastic telemark ski boots. It's a little awkward until one gets used to it.