To start off, the easiest way to look good on the field is
a tunic that comes to your knees before belting:
http://www.dagorhir.com/forums/index.php?topic=5902.0 (the armpit gussets shouldn't be 10" on a side, more like 6".) You only need around 3 yards of material for this; old bedsheets from Goodwill will do in a pinch, too.
and a pair of basic pants (sweats or scrubs will do, drawstring pants with a gusset made of a lighter material feel better).
Add a belt and brown or black shoes and you will look reasonably medieval! A
simple hood and
leg-wraps would take your basic garb to really snazzy quickly.