A quick and easy box-kite with only a single spar. Most of the materials you need can be recycled from your local supermarket or burger joint. My local supermarket sells fresh pies in flat-bottomed bags, takeaway bags also work well, but this version uses two of the brown grocery bags given out by American supermarkets.
Note: I originally wrote this Instructable in 2007, and only used black-and-white diagrams. I decided to update it in 2012, when in San Francisco, and all our shopping came in paper bags instead of plastic carriers. For the sake of history, I have attached a PDF of the original version, but don't feel obliged to read it.
Step 1: You Will Need...
Two clean, flat-bottomed grocery bags, quarter-inch dowel, sewing thread, and glue. The only tool I used was my Leatherman multitool.
You can substitute your own materials wherever you like (for instance, you could use the bag your burger came in, and the straw from your drink instead of the grocery sack and dowel).
(Irony: I used sewing thread to fly this version, but as we walked on from our test-flight, we found an abandoned reel of kite-line.)
Step 2: Make the Sail.
Open the bag out, carefully, into a sort of box shape.
Cut round the two short sides of the base, and one long side.
Lay the dowel inside the last, uncut, long side, sticking out at both ends.
Trim the dowel so that about an inch is sticking out at each side (remember symmetry).
Fold the base of the bag into the bag (over the dowel) and stick it down, trapping the dowel firmly in the crease.
Step 3: Make the Winder
Cut another piece of dowel, slightly longer than the width of the handle.
Fold the ends of the handle over the dowel, and glue in place.
Cut a length of sewing thread, and double it up (if you are making a small kite, one thickness is fine, but this is a larger kite and I wasn't sure how hard it would pull). Tie one end of the doubled thread to one end of the dowel, then wrap it around the dowel in a back-and-forth figure-of-eight fashion (look at the photo).
When you get to the other end of your thread, tie on a simple paperclip.
Step 4: The Bridle and Clutch
For this kite, the best length of bridle is about three times as long as the width of the kite.
File a small notch in the end of the dowel, tie on the end of the bridle, and add a drop of glue to lock it on.
At the middle of the bridle, I usually fit a device I call (for no reason I can think of) a "clutch". As far as I am aware, I am the only kiter that uses devices like this, in spite of their startling simplicity.
The clutch is designed to stop the end of the flying line sliding uncontrollably along the bridle, whilst allowing easy adjustment in the field. For this kite, it is simply a short piece of one of the handles. I cut two short slots in the piece of handle, then threaded the middle of the bridle through the holes. This provides enough friction to stop the flying line sliding up and down, whilst being easy enough to adjust in just a few moments without any tools or having to take the kite apart.
Step 5: The Tails.
Many long floppy things will work as tails - pieces of ribbon, scraps of left-over tinsel, or even lengths of video cassette tape - but for this kite I used the second grocery sack.
I laid the bag out flat, and then cut across the bag to cut it into eight loops.
I opened each loop out into a strip, then glued pairs of strips together to make four tails.
I glued the tails inside the back of the kite (one in each corner), and the kite was ready to go.
Step 6: Flight
The whole family went to test the kite - Roger-X helped fly it, Conker-X took photos, and Kitewife took some "me time" in the sun.
Technically, we used a high launch to get the kite airborne, but it wasn't a very high launch, because we were keeping the kite low enough to be photographed.
It flew quite well, until I trimmed the tails by about a foot, then it flew really well.
This is a great kite to make with kids - easy to make, and easy to fly, and so cheap it's not a massive stress if it gets eaten by a tree