I occasionally put my mobile phone or my car keys down there (not much room left in a G cup!).
I must stop doing that, though, as one day recently, I'd unlocked my care, then gone back into my place of work (everyone had already gone home), back to the car, to give a colleague a lift - I couldn't find my keys. I tipped out my handbag, pockets, purse, everything. I went back into the offices, checked drawers, toilet, under chairs, everywhere.
30 minutes passed, and I rang my husband, who (though annoyed), drove the 10 miles to me, to bring my spare car keys. Much later, after I'd dropped off my friend, I realised my keys had been in my bra the whole time! Him Indoors was not happy......