Each bike has a frame pump and a saddlebag with a multitool, patch kit and tube and rain poncho. I carry a medium chain in the saddle bag of two bikes and under the bag on the rack support arms of the third. I know I have too much stuff in my bag. But off the top of my head I have my helmet lights which I wear in the winter months, my main headlight, another patch kit (why?) pair of emergency underwear and socks, plus a polo shirt. One pair heavier gloves, sometimes two in winter, Extra headband. AAA batteries for bike lights, button battery for bike computer. Pliers, extra bungies and velcro straps, another rain poncho, plastic kitchen trash bag for backpack in rain. Sandwich bag for phone in rain. Reflective vest for night riding. Wind-breaker in summer months. USB cables. lightweight bellaclava (even in summer...why?) two cardboad fed ex envelopes to bungie to roadbike as fenders if caught in rain. $20, half in singles for emergency bus fare or whatever. Glasses case for tak-a-look mirror, extra glasses strap, extra micro usb for helmet cam. Notepad with pen. I keep shoes and coats at the office, so I will take my work clothes sans shoes and jackets. In the fall and winter I always bring an extra sweatshirt and one extra atheletic pant layer than I start out with, just incase I have to stop and hoof it. In the winter the bag weighs 25-30 pounds loaded for work. In the summer it's 18-23 pounds. On the weekends for leisure rides, it's like 10-15lbs, or less. I ride for fitness, so I'm not a weight weenie. However if my commute became more than my 9 miles each way, I'd think about paring down a little.