First line of defense: try to avoid the craving. Drink some hot tea, take a walk, do something that will take your mind off it. PMS cravings are tough but you still have to work towards controlling THEM, instead of letting THEM control you.
Second line of defense: Something IP friendly that meets the craving. If you crave salty, the dill zippers, southwest cheese curls or white cheddar crisps are great. For sweet, Holly's suggestions are great - for a faster fix, keep a bag of the Chocolate Soy snacks around. Figure out what flavor your body is going nuts for, and then try and find something close that's on plan. I used to crave pizza something awful - so I learned how to make flatbreads with the IP tomato soup packet, and topped it with a teeny amount of Veggie Shreds to make a little personal "pizza" - worked like a charm!
I have found that half the battle on this diet is the mental one. Cravings are not real hunger, and you CAN master them