I always pick up cable ties in the street - the ones the council drops there are much better quality than the ones in the pound shop.
Does anyone else have trouble stopping them springing out of your pocket? To my shame I've suffered this for 40 years before I realised that if you give the tail a half turn before putting it in the head (like a Mobius strip) it doesn't lock and doesn't try to escape.
Cheers.
(the rubber bands that posties drop are top quality too)