Stretching, ice, medication are all great. I would add a couple of things.
First, get custom orthotics. Wear an hour the first day and add an additional hour every day or two afterward. You won't have them ready for your trip , but it will help for the future.
Second, stretch the calf as explained above. Also add standing (not full weight) on a dowel or rolling pin for a few seconds at a time. Let the curve fit into the arch of the foot to help stretch that area out. Make sure you get down into the heel. Follow with ice.