Ooh, what an interesting subject!
I have often wondered what kind of underwear Indy wore underneath his clothes.
Some time ago on COW, this very same subject came up and I replied with:
"I have always been of the opinion that he would have opted for something comfortable with freedom of movement and am of the opinion that he wore boxer shorts when playing our favourite adventurer!
I think that silk boxers would have been the best option from Indy's point of view. They were cool (think of all the hot countries that Indy travelled to) gave him freedom of movement and when things got really romantic with the ladies, he'd be able to impress them even more!
Oh my goodness. I can't believe we're discussing Professor Jones' underwear! What would our hero think?!"
Shame these weren't around in the 1930's.