Cheese evolved - centuries before refrigeration - as a way to preserve milk. In general, any firm cheese worth eating should be able to hold up in a non-refrigerated environment for at least 20 hours, without a freezer pack and without being frozen.

We are not fans of freezing cheddar cheese, in general. It dries out and becomes crumbly when thawed. That won't happen if you freeze it for a very short time, but again, we don't think you need to bother for the length of your trip.

American cheese, being a processed cheese, has its share of preservatives. All the manufacturers of American cheese ask you to refrigerate it, except Velveeta, which wants refrigeration after you open it. Speaking for ourselves, we would feel very comfortable keeping American cheese out of the refrigerator while we traveled to Europe. Your concern is that mold will grow on the cheese, and we just don't think that is likely if the cheese skips refrigeration for one day, especially if you buy a package of individually wrapped slices. Our government would not want you to keep even processed cheese out of the refrigerator for longer than two hours, but the decision – and whether to use a cooler and freezer pack – remains with you.

Finally, while Germany is not, perhaps, in quite the same league as France in terms of cheeses, it is one of the great cheesemaking countries in the world, and situated in the middle of most of the other great cheesemaking countries. Your son has access to great cheddar cheeses and many other superb cheeses (some of which we can't get in the United States) right where he is. We have even seen American cheese in some supermarkets in the larger cities. We understand the desire for some of the familiar tastes of home, but we would encourage you to take your son out cheese-shopping during your visit, so he can acclimate his tastes to some of the great cheeses he has been missing – perhaps without even knowing he was missing them!