I have a fairly complete selection of SeaLine dry bags. As primary bags they're extremely tough, durable and waterproof. As secondary bags, I find large heavy duty gargage bags (orange, blue or black) are a lot lighter and easier to pack if just a waterproof membrane in needed inside a pannier. ZipLocks are another indispensable - particular for food suppies. I tend to use rain covers and garbage bags over anything I'm concerned about fading due to UV exposure too. They're easier to replace.