And there was me thinking that having useful subjects would give you a good start in your further study.
Yes, of course.
But there are two distinct aspects to 'useful subjects'.
The first is what general skills can you develop while doing an A level.
The second is what specific knowledge to you gain.
For some degrees, you have to have a combination of the former and latter - if you want to do physics you really need to have a grasp of both the skills and content of A level physics and maths, for example. You need to hit the ground running, they're not going to teach you from scratch.
For other degrees there's no assumed prerequisite knowledge. Geography is one of those - I know someone who did it at Cambridge who when wondering which of physics, maths, engineering lit or geography she should drop, was told she didn't need the latter as they'd be teaching her all the geography she needed. In the event she dropped the English, but the point is the maths, physics and 'an essay subject' were the useful skills, the content of whatever topics were covered in level geog wasn't needed.
So, first thing a student needs to figure out is if they're likely to want to do a degree that does have specific A level requirements.
If not, then think about what range of skills their choice of A levels develops , combined with some idea of how well they're likely to do in them.