Here are a few, nice not quite essentials. Foil and a baking pan/cookie sheet.
Baking pan is great place to set meat. I set it on a baking pan to rub it, I set it on a baking pan in the fridge (so no juice gets on a shelf), I set the hot meat on the pan to move it (abet often I should drop it in a chest), I could also wrap on the pan. Foil is a good way to cover the pan so it stays clean. Line pan in foil before rubbing - put meat on pit, throw away foil, clean pan. Line pan with foil to get meat... Foil can also be used to wrap meat during the cook, and for holding meat in the ice chest (abet paper works for this too). I also sometimes use wax paper instead of foil for the unheated part of prep.
Cutting board helps the table top last longer.
Definately not a necessity - but a vacuum bagging machine can not only let you split bulk meat into cook-able servings, and help freeze leftovers - it is also very convenient for marinading and brineing. W/O the vacume bag machine - ziplocks and plastic bags are practically an essential.