Urgent help needed - Interview Tomorrow

Capital markets is essentially a mix between IB and S&T, so you can talk about how that appeals to you by mentioning how you understand it is this kind of mix that will allow you the best of both worlds. Basically, know what an analyst in Capital Markets does (not sure if you're doing equity or debt so know both) and explain why you would enjoy doing those tasks / be good at them.

For why RBS, it helps if you have spoken to someone at the bank, preferably in capital markets. If you haven't, go to their website and find out about their corporate culture. Maybe say that while it is a BB (I think?), it has the feel of a smaller firm that will allow you to work more closely with your team members in a more close-knit environment (typical answer to give to why ___ (enter boutique bank name).

Hope that helps. At the end, ask the interviewer why he or she likes working at RBS (if you advance to second round, you can use their response in future interviews when asked "why RBS?").