Provided you have finished all the train-related quests (more abot them here), now you can order a Cooler for your second Railcar.
There are two ways to get a Train with a Cooler:
#1: Regular Train
The Cooler is only found in the second Railcar of your regular train. Order a Second Railcar (costs 1 Train Ticket) from your Train Timetables menu, then choose the “1 Cooler” option.
The second railcar is a one-time thing, meaning if you want the train to come with a second railcar again, you will have to use another train ticket.
You can add a maximum of 150 recipes inside 1 Cooler.
#2: Cheap Train
A Railcar with a Cooler comes every 3 Cheap Trains you call. If you need to sell Recipes, just send a few empty Cheap Trains until one with a Cooler arrives.