The paper on your living room floor was waist-high. That tossed-aside wrapping – ripped off the presents in 2.5 seconds – was a good indication of a good holiday, and everyone was content.

The mess that was left, though, begged the question of where to put all those new things.

In Adam Minter’s new book, “Secondhand,” the answer is always a little complicated…

Most of us have a lot of stuff, and our houses are full. So, Minter says, are our garages. A 2006 study indicates that “90% of garage space is now used to store stuff, not automobiles.” Our gathering and keeping has gotten so bad that businesses have sprung up to deal with what inevitably happens when personal belongings become an overload of unwanted items that someone must reckon with.

In Minneapolis, Minter found one example of the solution to the deluge.

Empty the Nest helps seniors downsize, hoarders let go and surviving adult children clean out parental homes. Discarded items – which, he discovered, could be family treasures or antiques – go to those in need or to a thrift shop where they’re sold to people looking for such things. Ultimately, discards might go to landfills, but every effort is made to recycle before that happens.

Goodwill Industries (“the king of an American thrift trade”) runs another kind of secondhand enterprise, relying mostly on donations from the general public. Goodwill’s efforts to reclaim items include boutique stores and outlets for the items least wanted. The author states Goodwill helps “divert more than 3 billion pounds of stuff from the trash heap annually.”

From Japan to India, rag pickers to rag-cutters, Minter explains what happens to our discards and where our excess goes when we toss it. This underscores one important point that should give every shopper pause: most of that which we own is worthless to everyone but ourselves.

That’s a notion that’s really quite sobering: all those antiques, heirlooms, papers and old projects you’ve been saving for the kids someday…? Chances are, the author says, they’ll go to the thrift store when you’re gone or to a business that deals with the detritus of life. Once you’ve read “Secondhand,” the presence of that fourth spatula in your kitchen drawer seems a little wrong.

Yes, you’re probably already familiar with thrift stores but there’s more to them than that 99-cent vase; as Minter shows, they’re part of a relatively-hidden network of businesses that handle what amounts to a genuinely shocking weight of accumulation. Those and other such companies opened their doors to him and answered his curiosity, thereby teaching us what not to donate, what not to purchase, why most stuff is worthless, and why too-much-itis is a problem around the world.

If you are curious, downsizing, or trying to be a conscientious consumer, you’ll want this book. Having it on your shelf is perhaps the ultimate irony, but that’s exactly where you’ll want it because “Secondhand” is not something to toss aside lightly.

Terri Schlichenmeyer’s reviews of business books are read in more than 260 publications in the U.S. and Canada.