A good way to prepare for any research trip is to write up the information you already have, as if you were going to submit it for publication. You don't have to submit it to anyone, but just the fact of writing it up, organizing it, and making your case and summarizing the details you know will get you on track for continuing your research and noticing holes.
I've often pulled up old Ancestry articles I have written to use when at a library when doing research.
Your writing need not be fancy (but it should be sourced). And your written up summary is better to take with you than just untranscribed copies of your records.
