How to prevent coffee from staining teeth while out?!

I drink coffee every day. It varies how many cups I drink, but my problem is that I drink coffee out of the house so I can't exactly brush my teeth. Otherwise, I always brush my teeth in the morning and at night. However, there's a huge interval of time in which I am in the office and cannot do anything about coffee possibly staining my teeth. I know the "drink through a straw" trick already, but is there a more proactive way to prevent this? Would gargling with mouthwash help? Basically, if you could offer some tips on how to get rid of coffee residue from the mouth outside of the home, that would be great! Thanks in advance.