What to take to the Immigration Visa Interview (in London)?

you don't have to go. however, it's usually better if you do, especially if there's a question about your residency. so, you don't actually have to be in the US at the time of the interview either. the officer may ask you to sit down while interviewing your husband, but won't necessarily. while there are many ways to establish residency the bottom line is that if you intend to go to the US to live with your spouse, that's good enough, uming the officer believes you. take whatever you have that you think proves your relationship. they probably won't look at it all, but it can't hurt to have it, just in case.