I'd call it being responsible, at least you're being careful in the event that a guy you like didn't bring one. Maybe in the head of a bloody traditionalist they might immediately think 'slut' but it's better to carry a condom or pack around with you rather than get yourself pregnant for being too careless.

If you ask me, the ones who get themselves pregnant and try to blackmail the men they sleep with for child support are the biggest sluts. Though that's because I've heard horror stories about men who have been screwed over by random encounters so that's my perspective on it.