Take some advil or tylenol at home and you can get one of those warmers (like when you go skiing) and put it in a hoodie pocket or something to help ease the pain.

Ibuprofen is actually far more effective for me than taking Tylenol or other pain relievers.  Many doctors recommend taking 800 mg Ibuprofen every 6 hours for cramps.  That is 4 of the over the counter Ibuprofen (200 mg) every 6 hours.  It should not be taken more often at that dosage and for not longer than a week.  Ibuprofen can also reduce heavy bleeding in addition to reducing cramps.  Be sure to check with your doctor for any medical advice...this is just what several doctors have told me and what I have found works.

 I've heard that eating bananas will help lessen menstrual cramps

Taking midol can help a lot with cramps/bloating.

When I was in high school, schools still allowed us to carry Tylenol or Ibuprofen as we needed.  We were even allowed to carry OUR OWN prescription medications.  I'm guessing you have to leave all of that with the nurse, now.  Exercise is my preferred method of dealing with cramps, as much as we really don't feel like moving when they strike.