I've also found the XXL and XL Ziplocs at the home depot when the local supermarkets didn't have them.
I pretty much use the Gallon, L, XL, and XXL depending on what I'm brining or marinating.
The XXL inside the bucket first, in goes the turkey, then the brine. Work the air out as you pinch to close, twist then I tie/loop - you can use a cable tie as well. Then seal. You can then leave in the bucket in a separate fridge, iced cooler or pull and place into another container, tray, roasting pan, etc.
Makes moving it about from one area, pot, etc much easier.
Nice clean set up. Allows you to use a smaller pot, different container depending that might fit into the main fridge better if you don't have a separate one.
Work great. I like using the XL and XXL even when I'm using a bucket or large pot.
The turkey bags work fine though if you can't get the Ziplocs.