I dove all week 4 dives a day in a 3 mil. I got a little bit chilled for a few minutes in my very last night dive while there so as far as I am concerned the 3 mil was great. I did bring a skin just in case to wear under the suit but I never needed it. If you chill easily you can always bring a core warmer type piece or a vest as backup but I doubt you will need it. Can't hurt to throw a hood in just in case and those smaller pieces won't take up much room.