You can get 24 hour heat packs. They typically cost a couple dollars. You will also need a cloth bag or a pillowcase to place the snake in, and a rubbermaid box with air holes.
Place the snake in the cloth bag/pillowcase, place the pillowcase in the rubbermaid, and finally put the heat pack in the rubbermaid. Since you are using public transit, you may need to "live animal" labels.
Hope this helps.