I have a bike with threaded holes in the frame but no bottle cage, so instead of buying one I made one from a yogurt container.

Step 1: Supplies and Tools

To make this bottle cage, you need:

The kind of bottle you want to carry on your bike to use as a template
A plastic container with a bottom larger than your bottle: I used a 1 kg yogurt container. Note that the container should be taller than the distance between the threaded holes in the bike frame (standard distance is 2.5 in / 6.35 cm).
Two M5 screws to attach the bottle cage on the bike
Tools: Box cutter, scissors, ruler, pen, stapler, screwdriver or Allen key (depending on your screws)

Step 2: Remove the Rim of the Container

Start by cutting off the rim of the container.

Step 3: Cut Open the Container

Make a vertical slit in the container, from top to bottom. Then, make symmetrical cuts along the bottom on both sides of the slit until you can wrap the sides around your bottle. They must overlap by at least a few centimeters. You will need to have enough space to cut screw holes in the overlapping part.

Step 4: Cut the Shape of the Cage

Use your bottle as a template to cut off the edges so that they do not overlap too much (mines overlap by 6 cm). Then hollow out the sides and cut out a rectangle in the front (part still attached to the bottom). Cut the bottom so that it does not stick out on the sides but leave some extra length at the rear.

Step 5: Screw Holes

Mark the location of the screws in the middle of the two side rectangles. The standard distance between the threaded holes in the bike frame is 2.5 in / 6.35 cm. Cut a small cross at each location. Fold the container to make the rectangles overlap and push the screws through both layers.