Every man carries different gear in his man-bag. Here's a review of a decent looking man-bag loaded up with gadgets.
My man-bag is very much akin to a woman's purse even though its probably not politically correct to say so.
first aid supplies
sun screen packets
USB memory stick
This is all the comes to mind at the moment. I could certainly add more items to increase my preparedness level but it suits me for the moment.
I, personally, am trying to stick with a small-ish bag because i carry it whenever I leave the house and I never put it down. I've found that briefcase and laptop size bags are generally hard to carry 24/7 and get in the way much more. My Fatboy is roughly 10"x9". I shoulder strap is an absolute must for me. I carried a day-planner for a few years but on numerous occasions I had to go back and look for it somewhere because I had laid it down while doing something else.
My first man-bag was a small shoulder bag that I needed to carry around my Apple Newton. The Newton was one of the very first PDA's and it was VERY large compared to today's micro devices. I kinda miss the large screen size though.