A great place to start is with The Guide to Liberal Learning that you got when you entered Brown. Perhaps the greatest credential you can take with you is confidence in your own ability. That includes your ability to explore and master new areas. Think about how you can convey that ability to others and you will realize that a transcript with grades is a relatively poor way to do it. Letters of recommendation from those who have witnessed your ability and can speak to it with solid examples are one effective kind of credential.
Communication skills rank high on the list of valued credentials.
You ability to connect verbally and in writing with others across a range of disciplines and levels is clearly crucial to your ability to convey your strengths and deliver your messages. A good balance of breadth and depth in your area of concentration is also important. Look for groups and sequences of courses that build a solid base from which you can move to a higher level of exploration. These serve as prerequisites for our 100 level seminars. Those seminars are largely taught at the graduate level.