Just about any bike shop or bike coop will have a bin of discarded inner tubes. Most places will be glad to give these away just to get rid of them. I like the long thin ones (27" racing tubes) for most ties I make. Making one takes about 10 seconds so you can keep some readymade or make them as you need them.
Step 1: Cut Inner Tubes to Length
I find 18" and 24" lengths are pretty handy, but the nice thing is you can make these pull ties any length you need.
Step 2: Tie a Knot in One End
Tie a single overhand knot close to one end of the tube segment and pull the knot tight. This will keep the slit (next step) from tearing out.
Step 3: Fold and Cut
The slit will stretch as you pull the tie tight so don't make the slit too big.
That's it! All done.
Step 4: Tie Things Together
To use the pull tie wrap the long end of the tube around something and slip the loose end through the slit. Pull this tight and it will hold fairly well until you want to pull it free.
Notice in Photo #3 that the right tie has the loose end tucked under the loop to make it more secure.