It used to be that newly married couples were expected to have their first baby before their first anniversary, and as a result of that, weddings and christenings were much more tightly linked to each other than they are today -- and, as it turned out, both occasions called for cake. During the 1800s when multi-tiered wedding cakes became fashionable, brides began saving the leftover top tier of the wedding cake to be used for the christening instead of buying a separate cake -- to be defrosted in what many a 19th-century bride hoped would be about a year. Today, couples freeze wedding cake for sentiment.
There's more to freezing the top tier of your wedding cake than a zip-top bag or food storage container -- or, we can barely imagine, in a cardboard box. The better prepped, the less chance your cake will suffer freezer burn. For example, before wrapping your cake, some recommend giving it a little time to chill uncovered in the freezer -- this is to help firm up the cake and frosting before you wrap it for storage. Wrap it with plastic wrap or aluminum foil and zip-top freezer bags (and if you gently squeeze the air out of the bag before storing it will help reduce the number of cake-ruining ice crystals that form). When the time comes, thaw your cake slowly in the refrigerator before eating.
Despite your best efforts, year-old frozen cake can lack a certain freshness, no matter how much care you give it beforehand, and modern couples have been known to celebrate the tradition with a freshly-baked -- and top tier-sized -- version of their wedding cake.