Facilitating subjects are not considered any more.
That said, Cambridge does have a list of recommended subjects for specific degrees (or categories of degree) so if that's possible it's worth a look.
Otherwise for sure there are subjects that are needed for some degrees. And if he is interested in those degrees then he should consider those subjects. But taking two old-school fac subjs in and of itself will not open up all degrees. I mean obviously.
So some examples of degrees and subjects you need
Engineering - take maths and physics
Science (inc psychology) - take the science you like and one other (but this can include the trad sciences, psych, geography, env science, even PE). (Not true btw that most science degrees require chemistry A level. DS2 has just graduated with a masters in bio sciences and no chemistry beyond GCSE.)
MFL - take the MFL
Eng lit - take eng lit
Medicine/vetmed/dentisry - take bio and chem ideally
CS - take maths
Economics - take maths and econ is a good idea too but not required
Maths - take maths and FM
But degrees like history (in a lot of unis anyway inc eg Leeds and Brum IIRC) geography, sociology, class civ, philosophy, criminology, social policy and many others need no specific A levels as a rule.
I see he has no idea – he must have a leaning towards some subjects? They would be an indicator of a good direction (eg no way DD would want to take biology A level so med/science was off the table - all good). Agree with others it might be an idea to talk to a careers adviser. And yy subjects he enjoys and will get a good grade in are a good idea.
I see from your update @Tomorrowtodaynever he says no to geog, MFL and English. That's all fine. And it gives an idea of direction. A combo like biology, chemistry and sociology or psychology would offer a lot of degree options - med/vetmet/dentistry/biology/chemistry/biosciences/psychology. Swap maths for the psych and you could also do chem engineering and economics.
Btw re English – it's not (at all) about creative writing (not eng lit anyway) and it is very much about reading books. DD in her eng degree had to read a book a week for each of three modules every term.
Apols for essay haha