i never ever leave my bag on public bathroom floors...i always hang it up on the door or have someone hold it for me. as for transit and such..i try to put it on my lap as much as possible and only put it on the ground if realllyy necessary. but even thennnn.... im sure my bags are still really dirty. =/ so thats why when i get home, i have a specific shelf and hanger to put my bags on =)