In general, universities in singapore tend to follow the british system of admissions more closely. There is a special emphasis on A/O level results above everything else, so other things like CCA/SAT/teacher recommendations don’t come into play that much.

If you are looking specifically at the com sci / comp eng (ie. hard science majors) in local institutions, then you’re pretty much required to take higher maths, chem and physics and get good A level grades in them. As for cca records and other accomplishments, they wouldn’t make that big of a difference unless the achievements at hand are really impressive to admission committees (eg. winning a gold at the international biology olympiad, setting a record at the SEA games).