Suggestions for incoming BB S&T SA

I'll be starting at a BB this summer for Sales and Trading. My rotations will be for exclusively sales desks. I have a good chunk of time before my internship starts so I feel as though I should be preparing. As an econ major with essentially no background in any types of products, markets or technical ability, how should I begin to prepare? How much will I be expected to know upon arrival in June? What books/websites/ programs would you consider essential to have as prerequisites for an S/T SA position? Also, any specific Excel or programming skills that would be advantageous coming in?

Any input would be huge, thanks in advance.