For Chemistry to be useful you really would need a second Science subject - either Biology or Physics for medical degree or related e.g. pharmacy. Chemistry and Geography would be useful if interested in environmental science.
Physics and Maths would still keep the possibility of Engineering open.
Economics and History would be fine for Business studies/ Law at university but would be more usual to add another humanity e.g Geography.
Both Physics and Chemistry are significantly harder at AS level than GCSE. It is also harder to do these at A level with double award Science - you really need to be doing the triple award at GCSE.