hulls, primers, powder, wads, shot.

A reloading manual
A scale

An area that's big enough to keep all of ^^^ organized. Depending on what type of press you have you'll either have to buy new "bars" for different powder/combinations or new bushings once you decide on a recipe. Or you can go the other way around...see what bars or bushings you have, then find a recipe that uses those bars.