If you want to prepare for bank exams, you will need to master:

Reasoning
Numerical ability
General Awareness
General English
Computer and Marketing knowledge
Database management skills

So for banking clerical jobs,  if it's possible take computer engineering. You can also graduate with maths or english as your subjects but then you will struggle a little with the computer knowledge as it is required nowadays in every bank.


For UPSC:
I think you can do graduation in BA in any field of your choice or Bcom.  You can start your preparation right after 12th while doing your graduation. You will have time for preparations too. Other courses like engineering, mbbs are very demanding courses and you will not be able to focus on other topics like general awareness.

Rest I suggest you take up your graduation according to your interests because these years will build you or break you. You don't want to join a course and then regret taking it even if it facilitates your preparation for govt exams. Hope I have answered your query.  If you have any more query, comment below.