Negotiating a faculty start-up package in biomedicine.

I am in the very fortunate position (and one that I previously thought impossible) of having potential offers from three R1 institutions. I have received verbal confirmation that I am the top candidate at each of these rather prestigious places (top 50) and have been invited for a second visit. I expect I will be asked to provide a wish list of space, equipment, personnel, etc. I would much appreciate any advice on how best to negotiate my package (not something that I have been trained to do). What is negotiable? What isn't? Should I ask for more than I minimally need given my position? Many thanks for your help.