We adopted a love of pasta and pizza from the Italians. We celebrate St. Patrick's Day because of the Irish Catholics. (Admittedly, we started celebrating it earlier than 100 years ago, but in Ireland, the celebration goes back to the Middle Ages.)
Our whole approach to Christmas is a borrowing from the way the 19th-century Brits began to celebrate it, and THEY were borrowing partly from Germans. Both Charles Dickens and Prince Albert, Queen Victoria's husband, were influential.
Many people today, in certain parts of the US, celebrate Cinco de Mayo even if they are not Mexican, and various Mexican and other Hispanic foods have become commonplace -- tacos, burritos, enchiladas, etc. Similarly, we've adopted various Asian foods as routine parts of our diets, and in certain parts of the US, celebrating the Chinese New Year takes place annually.
Opera and ballet were brought here from other cultures and have become popular here, like skiing and soccer among sports.