For the last ten years I've carried around a backpack for my jobs that contain a few personal items as well as random tools for work. Some of the items I carry:

• Laptop and tablet usually
• Mobile hotspot
• Chargers & cables for these
• Cables
  • USB to serial
  • Serial cable (for length)
  • Serial to RJ45
  • Sometimes random video, data and power cables (VGA, video adapters, USB..)
• Tools
  • Smaller screwdriver set
  • Normal screwdriver
  • Scissors
• Random stuff like screws, drywall anchors, velcro, etc

It's a bit of a mess and currently weighs 16lbs.

Never know what I'm going to need when I head onsite or even at my desk. I thought about getting a second bag to leave in my car but sometimes I take a work vehicle and afraid I'll forget it.

I have a larger more comprehensive bag at work but I typically only take this if I know I need something because it's a pain to lug around. It has a label maker, cable making and testing stuff, battery powered drill with drill and screw bits, additional random tools and junk.