As great as milk crates are, they still, in essence, are just open boxes. They tend to stack in the wrong way to store anything other than milk -- they interlock in such a way as to block access to the crates below, forcing you to break down the whole stack to get at anything at the bottom. To add a little utility to your crate collection, all you need are some industrial-strength drywall anchors, screws, and washers. By orienting the crates on a 45° bias, they turn into a self-supporting structural system while adding even more storage space in the "Vs" created by the vertexes.
If you just bolted milk crates to the walls at normal ninety-degree angles, each one would bear only on the one directly beneath it. By rotating them, you've created a situation where each crate bears on two crates beneath, a much stronger, holistic system. And, there's a nice aesthetic twist.
This project couldn't be simpler. It literally takes minutes to take up, minutes to take down, and leaves nothing but a few holes to be fixed up with spackle when you move on. The materials are (mostly) free, if you know where to look -- I'm not condoning stealing milk crates! They are legally available through many channels, including just asking shopkeepers instead of running off with them. I got mine through a combination of inheritance and combing through dumpsters and studio buildings at the end of the college school year.
You will need these materials:
As many milk crates as you see fit
3" drywall screws
Cone-shaped aluminum drywall anchors (50 lb. weight rating)
Washers of various sizes
You will need these tools:
1/8" or 1/4" drill bit, depending on drywall anchor brand
Philips head bit
Speed square or similar
Step 1: Put 'Em Up!
Score a level line on the wall. If you don't have a level, measure the same height up from the floor or down from the ceiling in two places, then connect the dots to make a level line, about the same length as the side of a crate, extremely lightly, in pencil. Then use a speed square or similar to take two 45º lines off of the level line. Line your first crate up with the lines. Drill into the wall with an 1/8" - 1/4" pilot bit through any of the open spaces in the bottom of the crate in two places, preferably at a diagonal to one another. Then thread some washers onto a screw so they will catch the crate, hold it up, and screw into the anchors, pulling the crate to the wall.
After that, it's easy. If your first crate is set right, all the others just notch against it. Start building your wall organically. For extra strength, zip-tie the crates together through the handles so they are a more unified unit.
As you can see by the opening photos, they can take a hell of a lot of weight. Some of those probably had thirty or more pounds of books in them, and there wasn't a whisper of movement for the whole year I had them up.