I lived near Kiel some years ago, so I can suggest a few things, with a big caveat: I have no idea of what the current restrictions due to Covid are. For that, check the other answers. But this answer of mine might come useful in the future, when hopefully the pandemic is over.
If you leave your luggage at the station, and don't mind walking a bit, you could have a Bavarian dinner and have a good homemade beer at the Kieler Brauerei if you want to walk 15 minutes (it's a bit more than 1 km; just follow the Sophienblatt, it's where all the shops are). It's quite large, so unless it's a Friday or Saturday night it won't be too crowded and I'm sure the staff won't mind you occupying a table for long, as there will be plenty of space for other customers.
If you don't want to walk that much, I think the Vapiano near the station is a good choice, because if I remember correctly it's a self-service, that is, waiters won't come to your table, you have to take a tray and walk to the counter to get something, so if you stay for long at a table the staff will probably not mind. They serve Italian food; nothing spectacular, but it's decent.
If you want to go to a pub, there are many, just pick one at random.
If you are into clubbing, the nightlife area is the Bergstraße, mostly between the Pogue Mahone and the SubZero. There should be the Luna (currently closed due to Covid) and a few more. Otherwise, closer to the station, I remember the Ben Briggs, where everything is ship-themed (check the pictures on Google Maps).