As for underwear, I find it odd that whenever a kunoichi's bra is mentioned in fanfic, it's usually something sexy or a t-shirt kind of bra, even on missions. Don't you think they'd be wearing sports bras? Especially the girls with bigger chests. I don't see any way Hinata could be running around on a mission in something that doesn't have that kind of support.

How about chest bindings? I've written a character wearing those, mostly because the unwrapping process is rather sexy. :)

Edit: And chest bindings do have that hint of kinky bondage fetishism to them too.

(Regular!Sakura wears something cottony and practical with a little lace to make it girlier, Akatsuki!Sakura wears naughty underthings as it's part of the Evil Organization contract, and Sasori goes commando, because a puppet doesn't need underpants!)