Learn pickup (or an applicable equivalent). A dedicated investment of three months, 4 hours a day, developing social skills will fundamentally alter your entire experience of university, making it far more enjoyable and far easier to succeed with group projects. There is probably no better way to develop confidence than through the repetitive humiliation and sometimes positive reception from approaching and interacting with hundreds of prospective mates. The associated skills and habits of interaction developed will do far more to further your career prospects than learning any technical skills.