Once you have your minimum kit, should you want to take on a battle field role (even as a non combatant), you will require a metal helmet which should be "fit for the purpose" I.E. not a thin reproduction display helm, they are good to look at but not for saving your noggin!
The cheapest helmet that you can buy is an old ARP helmet. They look like (and were designed almost like a fifteenth century Kettle Hat) which you can buy for as little as £10, but be sure that you don't buy a "tommy" helmet by mistake. (or battle bowler as they were known as) These had a much shallower bowl for the head to fit in and are not allowed to be used as they are blatently not right.
If you want to join in the mock combat the society rules say for your personal safety you will
need a minimum of....
a helmet :- as above
gauntlets :- I recommend mitten style as they offer best protection.
"adequate" body protection:-At LEAST a doublet but I would strongly recommend a padded jack,
it can be made at home or you can buy one for around £70 and it'll save a lot of bumps and
bruises.
To this list I would add...
A Bevor:-it might cost £50+ but it's cheaper than getting dental reconstruction. Accidents do happen so be prepared!
and, in addition you will need a weapon of some sort:- I reccommend a bill as they are cheap to buy and even cheaper to make.
Now the bear minimum equipment that you will need to start this Re-enactment lark will be your "soft kit", this is essentially the clothes that you can stand up in and will be what you need to get you into the "authentic" Living History camps.
Some items are marked with a * these you will find usefull to have more than one of (it's very authentic but not very nice to wear the same shirt for three days in a row).
Others are marked with a + as they are not essential but are handy to have.
Shift*
Kirtle (Dress)*
Coif / Headrail *
Belt*
Pouch*
Foraging / script bag+
Drinking vessel*
Eating set
Pewter spoon
Wooden bowl
Trencher (plate)
Felt hat
Woven hat
Shoes*