I would recommend Prime. Is the new water supply [ie ph n hardness] for you tank close to your old tank parameters. If not, depending on your fish, i would re-acclimatize them slowly.
I would recommend Prime, and most here do. But, I'm sure most other popular ones from reputable brands work fine. Just make sure you read what it actually does, as some remove/detoxify more things than others.
You can buy 5 gallon buckets for $4.25 at Walmart, plus a lid, then transport them in this wrapped in blankets to maintain temperature. Itf you 2/3 fill it, you will be able to reuse some of the habitat water for your new fish, usinng this when you fill the tank. As soon as you get home, you may want to put an aquarium heater into the bucket of fish and pop the lid to allow air in and out, or cover the bucket with some kind of mesh and remove the lid completely. This will buy you some time while you prepare your new tank. Remember to equalize temperatures before transferring the fish to the new tank and also to exchange water to avoid a chemical shock to the fish - that is when I would bag the fish and use the correct mixing technique during the release of the fish into the tank. I have 2 of those 5g Walmart buckets (from the decorating department) because they allow me to do big water changes using one for water out and the other brought up to temp and dosed with Prime and plant ferts before adding it to the tank. Cheap, clean and very handy!
I was told rubbermaid containers also work. Since I don't have the time to go to walmart (its 45 minutes away from where i live) I think the rubbermaid containers will do fine.