Many useful things come on reels. I highly recommend looking for those if it's something you'll need often. I do save string from sewn bags, like the paper bags of bulbs from Costco in fall, but those are thin. I have a ball of cotton kitchen twine. We also have a reel of coated wire that is great for securing things which need a little more support than a twist-tie.

In addition to take-home reels, you can also find things on reels at a good hardware store, such as chain, rope, and sometimes nylon strapping.