I'd recently re-tubed both of my bicycle's tires, as they both had leaks that were not worth fixing. After I was finished, I was left with two rubber tubes destined for the landfill... A perfect opportunity to recycle or re-use.
Simply cut the tubes into short 1/4" strips to get tiny black rubber bands
In the above picture, I'm using my paper guillotine, and have both ends of the two tubes tucked under the safety bar. I cut both tube just next to the valve, and again on the other side to remove the useless part. Once I had two rubber tubes (with some patches, natch), I started cutting.
When using a guillotine you need to press the blade against the cutting edge to get a clean cut through the rubber. If you don't get a clean cut, worry not, simply pick up the blade and try again, holding some lateral pressure.
After each cut, you need to prop the guillotine blade up, then hand-feed each tube a bit forward to get repeatable cuts. Perfection is not required, and you will destroy quite a few bands as you cut.
You can accomplish this with kitchen shears, but after a few minutes of cutting, your hand will certainly tire.