A light is obviously the best option, but when I need to transport my babies we use the "dragon mobile"
Here is Ruben modelling it for you:
Its a flat hamster enclosure I found at a charity shop for a couple of pounds, with a fleece on the bottom, then a half filled hot water bottle, then a blankie over the top.
I use this for all my vet visits which mean he's usually like this for about 3 hours.
Remember not to fill the hot water bottle up too much though or you will have one hot dragon!
Its better to have a little and ask to use someones kettle for a top up if it gets cold.
Holly