As you seem rather intelligent, based off of the subjects that interest you, I'm assuming you could take 4 subjects.
If you want to do Economics at Uni:
Essential: Economics, German and Maths. Beneficial: Further Maths/History. (I know you didn't mention economics a level in your post but it seems logical to take it if that's the route you go down. I also known that German isn't essential in terms of entry requirements, but having a foreign language in economics is a very valuable skill to have!).
If you want to do Maths at Uni:
Essential: Maths and Further Maths. Beneficial: Physics/Chemistry (or anything tbh, you could even do History and German and still get into a maths degree as only Maths and Further Maths really matter tbh).
If you want to do Medicine/Dentistry:
Essential: Biology and Chemistry. Beneficial: Maths/Further Maths/Physics.
If you want to do law:
Essential: If your school does law a level, it would make sense to take it. But you can do without it. Beneficial: History/German/Economics/English Language/English Literature. (I know you don't express interest in English lang and lit, but they're relatively common a level options for aspiring lawyers).
You haven't mentioned interest in studying a Physics based degree. However, if you do change your opinion on that this would be my suggestion for A levels:
For Physics/Engineering/Related Degrees:
Essential: Physics, Maths, Further Maths. Beneficial: Chemistry/German.
Hope I have helped in some way and good luck
...and how to stay positive