And it does happen that checked luggage can get delayed. So keep all your essentials with you in your carry on. Bring rain gear. Good walking shoes are a must. Be sure to include plenty of underwear and extra socks.
Laundry facilities are available, but be prepared to stand in line.
Most students in Oldenburg dress much like Americans. It's fine to wear jeans and a sweatshirt to class. On warm days, shorts are far more comfortable. German buildings are not air conditioned. A sweater is nice to have for chilly mornings or late evenings.