Mechanical repair (all stashed in an old water bottle): Multi tool (lezyne 5?), tube, tire levers, patches
The day's clothes (minus shoes, which stay at the office)
Lunch, usually in a couple of baggies and a couple of small lock'n'lock
Glasses x 2 (clear and tinted, wear one, other goes in case)
Granola bar
Keys, wallet, cell phone
Lights, which of course don't live in the bag
Garmin edge 500, also on the bike