1) Hand protection: Whether it be light sparring gloves, or the popular MMA padded glove protection, To-Shin Do training involves contact as far as striking goes. Having hand protection will soften the impact (everso slightly) when executing kata at controlled power, but full speed.
2) Chest/Torso Protectors: Though I don't find myself using them often, and haven't at any past seminars, test protection is something popular to where in To-Shin Do for the sake of adding a little force to the application of strikes. It really helps, I think, with the spontaneity of and intensity of the training session!
3) Shin and Forearm Gear: I've seen Anshu and some at the NC Quest Center wear these, and just from practicing the 'hicho' kick-stopping kata, having shin guards helps your shins alot! For those times during Earth and Water Element training, where punishing the attackers arm is part of the strategy, forearm protectors will minimize the numbing feeling of a strong 'fudo ken' fist into your forearm area.
4) Finally, Head Gear and Cage: Head gear is essential if you'd like to go faster with applications of 'head to face' head butts, as well as straight on elbow, knee, and punching attacks to the face or other parts of the head.
I'd say the most 'necessary' would be (at least for me) the hand protection, and maybe the head. I know how to recoil a little to keep my shins and forearms ok, and my partner's usually looking out for me in those departments, anyway. By no mean (obviously) would this gear substitute the necessity for focus target pads, kicking/knee shield pads, and the sort, when going for FULL BLAST power application. So with some hands and head, and a few shields (as far as it goes in my sessions) you'll be just fine!
Open palmed grapling gloves are my most often used item, both for sparring and weapons class. Certainly helps having some padding in between the back of your hand and a mis-judged bo/bokken strike that doesn't pull up a little short
head gear we use occasionally, but not all the time, I just use one of my Sensai's protectors.