Don't even think about using a pair of pliers to pull up the zipper on your favorite jeans. It's not worth the discomfort. Avoiding salt immediately before and during your period is also a good idea. Salt increases water retention. And it has happened to almost every woman.
First step is damage control.
Tie a sweater or jacket around your waist or untuck your shirt. If that's not an option, have a good friend walk directly behind you on the way to the bathroom. Find the closest tampon or pad . When you get to the bathroom, check to see if you can blot out any noticeable spots. If it's a hopeless situation, take a trip to the nurse's office and see if someone can bring you a change of clothes from home.