A cute container made from either a .5 mL or 1mL plastic Coke bottle. As a bonus, it makes a very satisfying snap when opened and closed.
I cannot remember who was teaching this at the Origami USA convention a few years back (2006? 2007?), but I seem to recall it was brought to New York by the Brazilian group. It was a huge hit because it holds models so nicely for gift giving.

Step 1: Assemble Parts

To start you will need:
1. Coke bottle of correct size (see Step 2 for selection process).
2. Sharp pair of scissors.
3. Rubber band (optional if you feel confident in your cutting precision).
4. Marker (also optional)
5. Fabulous gift to put in the container once it's complete.

Step 2: Obtain the Correct Type of Coke Bottle

It must be either .5mL or 1mL size with the "old school" style ridges up the sides (not the new design with the swirls and bumps). You might also be able to find green Sprite bottles in this shape and size.
Sadly, the tiny size bottles (I'm not sure of the volume, but they look like a squat version of the medium and large sizes) don't work. If you discover a way to make the tiny ones work, PLEASE let me know!

Step 3: Cut the Top Off

Using sharp, pointy scissors, cut along the bottom of the label. If your bottle has no label, cut along the slight indentation that runs perpendicular to the ridges.

Step 4: Place the Rubber Band

The band needs to sit at the narrowest part of the bottle. If you want to check that it's in the correct spot, it is about 2 inches from the base, or 1 inch above the horizontal seam (see second pic).

Step 5: Mark Where to Cut (or Not)

There are 10 vertical ridges. You are going to make 5 cuts, 1 on every other ridge. If you want to make sure you're making the correct cuts, mark every other ridge with a Sharpie. Only mark to the band.

Step 6: Start Cutting

This is where your container will succeed or fail and it's truly a fine line between the two! Cut ONLY to the band! If you cut too far down, the snapping mechanism won't work and the bottle won't stay closed. That said, take a deep breath and cut 2 ridges. Test the flap by pressing it in towards the middle. If it's cut correctly it will stay folded down, then snap back up when you unfold it.

Step 7: Test All Flaps

Fold all the flaps towards the middle to test them. You may have to adjust the cuts a bit, but please be conservative! Seriously, like 1mm at a time! Oh, and you can take the band off if it has not removed itself.

Step 8: Shaping the Flaps

If you don't like square flaps, you may cut them into a more rounded shape if you like. I've tried cutting the flaps into a pointy, triangular shape, but it wouldn't stay closed very well. Ah, well. Anyway, you can experiment with all kinds of shapes and see what works.