A Level Economics can complement any subject at A Level. It works well with Science courses as it uses similar processes but adds sophisticated analytical skills to your essay writing technique. It also works well with Humanities like History but develops a more scientific approach. Economics could also be a good fourth subject for a student trying to build a broad portfolio of subjects.
If you think that you might want to continue to study Economics at university, you will almost certainly need to take Mathematics at A level. For the most selective courses Further Mathematics is desirable.