I'm a big fan of these and these, both from Survival Resources (by John McCann). The former are very robust and pack down into an extremely small space. The latter are very, very durable and can be used for fairly long term use.

The only gripe I have is that there's a "handling" charge over and above the shipping cost. That's a crappy way to conduct business, IMO, especially if you only sell online. It's like McDonalds charging you to put your "to go" order into a bag. Still, they sell good quality product and the service is good, so I don't like it but I deal with it.