I just sold my house, put my belongings in storage and have begun long-term travels overseas. I got rid of lots of things that might not fit into a new, smaller home (one that has yet to be found and purchased), and what I kept (books, arm chairs, side tables, kitchen stuff, wall hangings, rugs, etc) are things that I love.
After emptying a 4BR/2BA house (including the single care garage and a garden shed), I ended up sending 3,800 lbs of belongings to professional storage. It will cost me $140/month.
I highly recommend professional storage. It's climate-controlled, has good pest controls, has fire and flood protection, and is insured. Yes, I could have used a relative's barn for storage, but I got rid of the stuff that was extra (things that I actually didn't like, that wouldn't store well, that were in poor shape, or that were fairly large sized), and I didn't want to risk - for example - my books getting moldy.
During my time working for the federal government my colleagues and I were frequently posted overseas for a few years before returning to the U.S., and during those years we were overseas our belongings were placed in storage. Those who initially used extra space in the houses of friends or relatives to store a few special things normally ended up regretting it.