I almost always carry some ground kava root with me when I leave the house. I keep four (400mg) capsules in a military surplus personal first aid kit when I'm working (I figure that if I ever need a lot of the stuff in there, I'll also need something to calm myself down and mmaybe somebody else) and I keep a jar of the stuff in my book bag for my own personal use, a friend of mine who has frequent anxiety attacks and anyone who I come accross that might need some. The fact that I'm often seen handing out pills to people in public places has lead to a joke (or at least I hope it's a joke and not something people actually believe) that I'm a drug dealer. That reminds me, Kava is restricted and outlawed in a number of countries so check online to see what it's legal status is where you live.
I've found that a couple capsules help me relax enough to keep doing whatever I have to do without inhibiting my mental clarity. Bear in mind that taking too much will put you right to sleep and it's been known to cause serious liver problems (which is the main reason it's banned in so many places). That's why I keep it in pre-measured tablets or measured out in tiny plastic bags & mixed with some milk thistle.
Alcohol can also be helpful depending on the nature of the situation, but just don't drink and do kava around the same time. That's a sure-fire way to do permanent & potentially VERY serious damage to your body. I've also found that self-medicating with a number of other substances has helped me continue to do the things I have to do on a daily basis, but some of those were controlled substances attained via legally ambiguous means...
Other than drugs, I use all kinds of s**t. I actually carry around a big piece of amethyst in a backpack most days because it's believed in new age spirituality to be extremely calming if you're open to it's vibrations. I don't know if I'd go so far as to say I really believe that stuff, but I don't see how it could hurt. More information on that here: charmsoflight.com
Of course, when a situation gets really bad I just get the hell out of there. That's probably the most ideal option, but I know that it's not always possible...