For us it's being very mindful of what we do purchase and try to live "lightly". We have an elementary aged son and he is in no way deprived but it's amazed me to find he was happier with less stuff- the things he has, he loves and really cares about. Before we moved to a lighter lifestyle he would tell you that such and such toy was boring and he didn't want to play with it right now-yet there it was taking up space (physical and mental) and it would hang around waiting to be played with. Now everything is just easier (to clean, to care for, to play with, etc).
Yes--exactly--for us it is not about having nothing or trying to have as little as possible; it is about consciously only having what we really, truly want and will bring us joy on a lasting basis.
So, as cool as subscription boxes sound, as as much fun as it would be to get them on the day they arrive--I would never do that these days: a boxful of things not chosen by me or someone who knows and loves me is highly unlikely to all be stuff I will really enjoy long term. Likewise--we almost never pick up swag on offer at conventions, etc.
We've always been big on one nicer gift for holidays instead of lots of little things to open, etc.
Then add in really thinking about if you will use an item a lot before you buy it (or, waiting a week to see if the desire passes), well, you end up with not so much stuff--and YES, we enjoy what we have more, and it is easier to clean and keep everything in order, etc.
And i am laughing at the books. I have about 30 leather bound books my mom gave me over the years when I was younger. They mean the world to me and are among the few things that we brought overseas when we moved here (we also shipped my husband's stereo and eventually had the antique regulator clock my father in law rebuilt and gave us as a wedding gift shipped over as well--those are all things which are not needs and have minimal use (the stereo has more use--but we could play music on a much smaller device I guess) but they all do bring us great joy and long lasting joy--so they make the cut
(oh and to the poster who mentioned Girl Scouts--oh yes I do love it. My daughter is in college now and i am still leading and the Overseas Committee Chair for our town--this is my 15th year leading---I think scouts has got a permanent grip on me lol)