We use one every day we're at WDW. I don't know the exact size off the top of my head, but it's a lot like this one, but a bit bigger...
https://www.webstaurantstore.com/ch...rier-black-nylon-23-x-13-x-15/124FCARRBK.html
We need that size since we pack for a family of 5. And yes, as Marionnette mentioned, we're one of those families that "go to that length" and use an umbrella stroller to carry it in. It's ridiculously easy and SO much better than using a locker. The cooler fits perfectly in the seat of the stroller, and 95% of the time we just park it somewhere in stroller parking (in the shade if we can) and just leave it. When we're ready to eat, we come back and get it.