Growing sprouts.

Keeping baitfish alive.

Appropriatley modified to present blunt teeth in front of a collecting hollow, a grain harvester.

Many impromptu wind and percussion instruments.

When filled, rollers, especially for very heavy loads. A two liter filled with sand is nigh on impossible to crush unless it gets pierced by some thing sharp on the outside.

Why not filled with water (filled all the way up, no air gap)? Water is pretty much incompressible.

In a good many scenarios, the overwhelmingly best application for decent bottles is to store or produce (a la SODIS) potable water. Crunched or broken bottles might be used for some of the applications discussed, some of which are rather far fetched and suboptimal.

Stretching the imagination when it comes to survival seems a good thing. Inhibiting yourself too much when brain-storming, not so much.

Cut the sides to make improvised fishing spoons.

Cut the screw top off to make an improvised gromet.

And for my fellow caffine jumkies, carefully cut one of the bottom "bumps", leaving a strip attached to make an improvised coffee scoop or spoon.

Sounds like you could carve 4 "spoons" out of one bottle with material to spare for "knives", etcetera. You may pretty much have created the other 'ware in the process of creating the "spoons." Nice idea!

"Necessity is the mother of invention!"

Yes, Mom!

Brainstorming, as I understand it and have practiced it, is not quite the same thing as a simple query... Had it been clear that brainstorming was requested,I would have immediately suggested that one can cut off the mouth of a narrow mouth pop bottle for use as an emergency engagement ring.

Inherent in the brainstorming process is the step where you have to get real, come down to earth, and evaluate all the responses. Suboptimal suggestions are inevitably inherent in the process.