Dave:

Unless you're planning to do much walking, I swear by shearling boots
(almost high-top slippers) in a larger than normal size. They're
available during winter in Costco for less than $50. They're slip-on,
so if you bailed out they would probably come off when the canopy
opens. I guess you could put some kind of tie around the ankle, but
any constriction of circulation will only exacerbate the problem. I
think Sorels would be good if you worry about bailing out and still
having boots when you reach the ground, but in my size they would be
much too large for most gliders -- my toes would hang up on the nose
of the glider. Think about the shearlings -- I put them on before
going to the flight line, and even when there's snow on the ground and
they get wet they still work very well in wave.