Went through the same exercise with my wife. It was my second time.
We emptied our apartment (which was rented furnished, specifically for this scenario) and our personal stuff we were lucky enough to be able to store in a friend's house.
We gave away a bunch of clothes and shoes, my wife in the beginning had difficulties but later in the process she got totally onboard.
Seeing the minimalist documentary on Netflix was very helpful too. We were starting the mindset but the documentary was great to reemphasize the philosophy and discuss between ourselves why we were doing it.
When finally starting the travel bit, we bought a cheap second hand car, our only curse is that we still have too much stuff. My personal theory is that no matter how small or large, your luggage (or car in this case) will always mysteriously fill up...
In 2010 I travelled a year throughout South America out of a 30 liter / 10kg backpack including a 2 kg Thinkpad laptop.
(Checkout Tynan.com for the ultimate in ultralight backpacking he has it down to an art (google gearpost 201X he usually is pretty up to date)
Actually I had the same experience as you describe, never really missed a thing, depending on climate I might buy some cheap t shirts or an extra sweater but overall I came back with roughly the same luggage.
It was great having such a small footprint, convenience wise and security wise, I could walk about in a major city and no one would know I had all my belongings in my smallish backpack. Never had to give up my bag to put it in the hold, where it can get stolen more easily, and always got on with handluggage on flights.