Recycling Cardboard Tubes

Fold an empty toilet paper tube in half, collapsing the tube. Open it up and fold it again in half, this time meeting the first two folds in the center, collapsing the tube again.
Cut the tube in half, forming two shorter tubes. Measure 5/8 inch from one cut end and draw a line, parallel to the cut edge, all the way around.
Slit each of the folds up to the line. Crease on the line, all the way around. Using this crease, fold all the flaps into the center of the tube and tape closed, forming a small, open ended box. Glue twelve or more of these small boxes together with a glue stick, forming a tray. Paper clip the sections together until the glue dries.
These small trays can be used for sorting and storing small items, such as nuts an bolts, beads, pins, bobbins, and so on.

What else can be done with cardboard tubes?

Many fabric stores get their fabric on cardboard tubes. These tubes are thick and very strong. They can be sawed and drilled, just like wood. They can be painted, glued, and bolted or lashed together to make furniture and other useful items.
They cannot, however, support screws, which will chew at the cardboard and weaken the joint quickly with use.
For example, we needed an easel for a display at a craft fair.
We had four of these heavy duty cardboard tubes.
We pressed the ends of three of the tubes together. It wasn't easy. If I remember correctly, we stomped on the ends, but they reopened.
We drilled a hole all the way through both layers of the tube, about two inches from the end, taking care to make the holes even.
We repeated the drilling with the other two tubes.
We pushed a long bolt through all three tubes, squeezing them together. We then added the nut. The three tubes spread out. We made sure they spread at the angle we needed for the easel to stand. Then we stopped tightening the nut.
We cut the fourth tube in half, forming a shorter tube. We drilled two holes in each end, all the way through the tube.
We drilled two corresponding holes in the two outer tubes of the tripod. We bolted the shorter tube to the tripod, making sure the new piece was parallel to the floor when the easel was opened.
Finally, we attached a rope to the three legs of the easel to prevent it from opening too far.
A good coat of paint, and no one would ever know this item was entirely recycled.