Oooh!
Rubber bands - I've got a whole bunch in my desk drawer but I totally forgot those! Will band up my cordage here in a little bit. Thanks! Hope we can keep this topic going for more ideas...
Rubber bands are good but they seldom last long. Even in near ideal storage conditions they can dry out and get brittle or turn into mush that smears and ends up everywhere.
A good alternative to the standard rubber bands is to drop into the hair-care section of the big box or drugstore and get 'scrunchies', hair and/or head bands. These are wound with thread that helps protect the rubber compound and the higher end versions are made of synthetic rubbers compounds that resist UV, oil and general wear for a very long time.
I have some in one of my kits that are over ten years old that are still strong and pliable. These are a bit over two inches in diameter and cost about $3 for a dozen in basic black.
The headbands are thicker and much larger. The ones I have used were about quarter inch thick and eight inches in diameter. Cost about $2 each.
While your nearby get yourself a shorty makeup brush, intended for blush, to use as a lens brush for glasses, binoculars and camera. These are great for getting sand and abrasive dust off those delicate lenses. Sand and grit are a problem when in the field in Florida.
The one I got is about 4" OA and weighs just a few grams. Cost a bit more than a buck. A real deal compared to the purpose built 'lens brush' which is about 6" long, weighs twice as much and costs $10.
Even in a small space constrained kit it can pay to include a tube of lip balm. Very few things are as annoying as chapped and cracked lips. Get the stuff with a sunscreen in it and you can at least protect your nose and lips. Big relief.
The wax and petrolatum base is a decent lubricant (trick is to warm the mechanism so it melts in), protects steel from rust, bits can be sliced off to get a fire going, roll up a bit of pocket lint and make a wick for a short-term candle/lamp, and it can be rubbed into the dried out cuticles to prevent annoying and painful bleeding hangnails.
Lots of utility in a compact package.