I worked with a guy who aspired to sail around the world. He was training his girlfriend to downsize possessions in order to fit on a sailboat. While obviously you need tons of food, water, parts, emergency gear, he'd told her, "You're ready when all your personal gear (including clothes) fit in one duffle bag."
I like to travel (airline, vacations) light and with two kids along, I use some tricks. Clothes that wash and dry quickly. Layers to customize for the weather. Many of the multipurpose tricks (e.g. phone = camera, map, copy machine, notepad, etc) that BPers use.
For non-outdoorsy trips I especially like to use "one-way clothes". There are items that I'm about to toss. Socks or underwear that just got a small hole. For fieldwork, an old shirt that I was about to retire. I bring those clothes but toss them out as I go. There were a few years when prior to a road trip or fieldwork for work, I'd let my wife pick out a few items she never wanted to see me wear again and it would make a one-way trip.
For the fieldwork itself, I've done a lot to refine my tool kit and instruments so I can do the most with the least. The problem solving on-site is fun and remember - just 30 years ago, all houses were built without a cordless anything. Or rather, a "cordless screwdriver" was the original cordless screwdriver. You know, just a screwdriver. So often I see a guy spend 5 minutes setting up an 6-pound power tool in order to do a job in 12 seconds instead of just using a 4-ounce hand tool for 2 minutes.
The most useful piece of gear for travel or construction has a portrait of Benjamin Franklin and weighs one gram.