Looks like they might be just the ticket to waterproof those standard panniers...
https://www.ziploc.com/Products/Pages/BigBags.aspx

Freezer grade bags are awesome as they are tough and can help organize your stuff... my panniers are just about as waterproof as can be but if you throw anything in that is damp it will mess up everything.

Garbage bags work fine also.

Before I got Ortliebs, I used garbage bags to waterproof and zip lock freezer bags to organize - (a touring staple.)

I throw what I can in zip locks, they also keep dirt off or keep it in a bag so the bottom of your bags don't start to collect it. I always keep a tube in a bag to hopefully prevent punctures.

Ahhh so! Another devotee of the mystical preventive spare inner tube!

Anything I carry that is beyond riding will prevent problems. Tube = no flats, wrench = no mechanical problems, etc. If I carried a professor on my bike I could prevent tests.

I keep large zip bags from different things, it's become a running joke with my co workers. They work perfectly for putting a change of clothes in and mashing flat, then tossing in the panniers.

Ziplocks, trash bags, grocery store plastic bags, they all come in very handy.

True. you can even use grocery store bags like rope to tie stuff down to your rack if you don't have any more room in your panniers.

I use zip locks usually to protect my cell phone when I decide to bring it along. It protects against rain, and sweat.

+1, and the wallet.

The 2.5 gallon ones work great on tour last summer. Used them to wash clothed in.

i used to find the old MEC shopping bags were very sturdy plastic and would not rip or tear as easily, so i used them to stuff my stuff i wanted to keep dry in my not so waterproof pannier. too bad MEC stopped using bags now. so now i just some contractor garbage bags cut in half to a reasonable size. those large size zip lock bags look neat, but are pretty expensive.

Large Ziplock bags are amazing! I use them for all sorts of things. My ski team kids use them to put their Uggs in for after meets. Keeps them dry and clean. I use them for traveling, heading to a retreat where we are probably going to be in mud, will put the dirty wet stuff in there and it will keep my suitcase clean. They last for a while so you can reuse. Also, those space saver bags that cost a fortune? Make them with the giant ziplock and duct tape. Put a small hole in end of bag, cover with duct tape, place items in bag, zip and roll towards end. When all air is squished out tape over hole and there you have it.

I use the small one as a wallet.

Also the grocery bags are used to cover my B-17 when I get caught in the rain.

Excellent idea. Thanks for this.

Love the big Ziploc bags. I roll up my clothing and then roll it up in the big zip bag, which then slides slick-as-you-please into my pannier next to anything else I might have in there. Great for separating stuff you want to quarantine from stuff you don't care about too -

+100 on the big bags - been using the same on for 2+ years now . .

The XXL version will hold 20 gallons. Ye gods! That's a lot of beef stroganoff!

Silliness aside, I've used the smaller ones for waterproofing (cell phone, TP) and food carriage (fig newtons), so I'd reckon the 3 and 10 gallon units would work just as well. Actually, it's a brilliant idea.

I've always wondered how these would work - would have to balance the re-usability against the cost, I'd think.

No..but I do use a shower cap as a raincover for my Brooks saddle.

I use one in my backpack on the days I ride the fun bike (no rack).

When I was using fabric panniers I found that the reusable, fabric shopping bags treated with a water repellent spray worked very well as pannier liners.

With my homemade hard-sided panniers I use smaller zip-lock bags for organization.

Eggs, ham, cheese, salt & pepper in a ziplock dunked in boiling water makes an easy omelette.

This actually works??
another great idea. Keep em comin'!