Cheap styrofoam coolers are your best bet. Bags with larger catfish are a bad idea, there are tricks to this, but I don't think you want to loosely wrap your large catfish with wet paper before placing it in the bag unless you are used to doing this sort of thing.
I've seen large cats turn fish bags into leaking torn up pieces of plastic without paper. It is fun to pull out the paper at the final destination & watch how fast they can do this though. Just one more fun thing you can do with fish.
Fill the styros about 1/2-2/3 of the way with tank water, put the fish in & tape down the lid. I've seen large fish knock off untaped lids. Make sure to keep incompatible fish separate. The insulated cooler will keep the fish warm enough unless you plan on putting them in the back of a truck in the dead of winter.