Natural Sciences can lead to subject specific jobs (usually with a masters or PhD after), or more general professionals jobs requiring an analytical and numerate brain (like banking, finance, big 4 accountants/consultants etc). On top of that, the big corporates looking for graduate scheme recruits will be going after science graduates far more than arts.
The salary and job security tends to vary by which of the above paths you follow. Staying as a professional scientist, after more specialised post-grad study, will somewhat limit earnings. Not bad but not as good as in corporate, or at consultant level, medicine. As a professional scientist nearly 20 years ago, my first job was £25k. Within 3 years it was £30k, then I generalised and in 2 more years it was £50k. Then kids, but that's another issue. (Compare that to tech/engineering jobs where a few years in you might be on 80k, or finance where you will probably be 100k+.)
Have a look at some of the big graduate schemes to get a feel for what's on offer there.
Civil Service is another one, aiming for Fast Stream (if he's looking at med and NatSci I'll assume he's heading for a top uni with high marks). Lots of demand for analytical brains in the CS and if you get through the exams, then you go in about halfway up the pay scale and rise quickly.
Friends of mine also with Nat Sci or similar degrees from top unis have gone into: Science, academia, publishing (science and fiction, journalism), Civil Service, officers in armed forces, accountancy, analyst positions, big corporate, banking, museum curators, all sorts really.