I've been cutting those 2L plastic bottles in half and sticking them into themselves, like this
No rhyme or reason for it, I just happen to have a box cutter on my desk and I drink a lot of fizzy drinks.
I keep telling myself that I'm keeping them for some future project, but so far I've amassed nine of these cut in half bottles in the kitchen and they're all just sitting there empty as the day I cut them, waiting, judging.