Each and every tire inner tube is a source for rubber bands. What we have in the photo is an inner tube from a 21-inch tire.
Some of the handiest items we come across are recycled motorcycle parts. Yes, really! For instance, motorcycle tire inner tubes make handy-dandy rubber bands. Inner tubes come in different sizes (depending on the size of tire tube) and have an unlimited range of uses, from acting as a cheap bungee cord for holding items on the sissy bar or luggage rack to holding your rain gear in a nice tight roll so it doesn't take up much room in the saddlebag. Even in the shop, these big rubber bands come in handy for holding a box closed for storage...or how about a couple of rubber bands wrapped around the vise jaws to protect a part from scratching? On the road, a couple of these bands around your tool kit doesn't take up much room, and are close at hand if you need them.
For those of you who have never seen a tire inner tube, they are not needed for a custom billet or solid wheel where tubeless tires are used. Inner tubes are usually used on spoke wheels, where if an inner tube is not used, air will leak out past the spoke nipples. Yes, we know there are some exceptions, but not that many.
To make a large rubber band, simply cut a section from the inner tube with a pair of snips or scissors. | 
Like we said before, one inner tube equals a lot of rubber bands. Different widths are no problem. If your friends have different size tubes, trade some of your bands for some of theirs. | 
Here we have a couple of rubber bands stretched across our custom rack. There is no limit on what these rubber bands could be used for. |
We keep a couple of rubber bands around each of the tool rolls on our bikes. We haven't needed them yet, but you never know. | | |