I leave mine out in plain sight.
No sense hiding them since she'll see me use them at some point.
I apply the same for everything that concerns my girlfriend. She knows I look at other girls when we're walking around, she knows I watch porn, she knows I spend more than I should on electronic gadgets and she's acutely aware of my tendency to upgrade every light-emitting item I come across (and plenty that don't emit light).
She, of course, has the same attitude toward me.
Personally, I find this the only way to live a peaceful relationship. Hide things and they're eventually going to be found, if only because you're not a specially trained secret agent and will eventually put yourself in trouble by saying the wrong thing at the wrong moment.
But if you don't hide them then there's nothing to fight about; if one of the two doesn't like something, you talk about it and reach a peaceful solution. Or don't, but at least nobody can tell the other one "you hid this, so you knew you were in the wrong".
As for the problem of spending common money, well, that's why I consider it an awful, awful idea to have a joint bank account.