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Wet a bit of cordage (to prevent burning) and tie it around the lip of a partially filled bottle (you don’t want it to boil over and douse the flames). Suspend close enough to your fire that flames lick the bottle. Nutritious upgrade: Pop a few grubs or worms in there.
Place a bit of dry-rotted wood, cotton, or linen cloth inside your bottle and lay it flat on some fire coals. (Note: Don’t pack the bottle full or it might explode.) Once the material stops smoldering, use a green stick to fish the bottle off the heat. Charred tinder like this ignites easily from a spark (unlike a lot of natural material), but won’t flame up, so you’ll have to place it in dry tinder and blow to coax up a flame.
Carve a plug from a bit of green wood if your bottle lacks a cap.
Start a fire.
Harness the sun (like with a magnifying glass) by filling the bottle with water or other clear liquid. Cork the end with your thumb and hold the bottle horizontal and close to the ground. Fiddle with the angle to concentrate sunrays onto your tinder (see left).
Hone your blade.
Grip the bottle by its neck and place it on a flat surface. Place your blade so it forms a 20-degree angle against the bottle and push the blade away from you. Flip the blade and, maintaining the same 20-degree angle, pull the blade toward you (carefully, but this technique is more effective) to sharpen the other side.
Stab, cut, slice, etc.
No use crying over a broken bottle. Shards work as knife blades, spearheads, and strikers for firesteels. Just make sure to protect your hands.