In Washington and Oregon, the processors are not allowed to freeze the birds. They are chilled to 38 degrees then bagged. Those very large white coolers you can buy at Costco hold 25 broilers. Then I cover them in ice for the drive home. I keep them in ice until the following day when they are sold at the market or distributed to pre-order customers. I am not allowed to freeze the birds, either, if they are for sale. This falls under 'processing'.
I haul mine loose in the back of my pickup, which has a canopy. I put straw on the bottom. I then load them into crates at the processor. It's a bit of a juggle taking two of the coolers plus filling the back of the truck with live chickens. So, I have a small trailer I take to haul the coolers in when doing more than 25.
For our own birds, we usually use the FoodSavr and vacuum seal them for the freezer.