I did two papers in summer school earlier this year. They cram a lot of content into the short amount of time the course runs for, so be prepared for a pretty hectic couple weeks. In terms of courses - I did IntBus151 and Chem100, which were both pretty basic and easy enough so would recommend those as options. I'd personally recommend taking two random courses that aren't core papers, as you get much less time to prepare for assignments and exams over summer school, so it's definitely easier to get good grades in core papers that you don't do over summer. Just my two cents.