I have no idea what to get my stepchildren for their birthday

My husband has twins who are about to turn 17. They are boy girl twins and these twins are some of the most independent children I have ever met. They both have a student savings account and started working at 14 at Braums(an ice cream shop). His son works at IHOP as a server and daughter works at a daycare. Idk how these kids work and maintain A's and B's and still have time for activities. They are so independent and great at time management. Idk what to get them because they buy everything for themselves and if they don't have it they will just save and get it for themselves. They are very independent young adults and have pretty much anything a teen could want and bought it themselves. I'm stuck on what to get such independent teenagers. Any ideas?