In the absence of PMS issues [I am male] I used to suffer from the sudden onset of migraines- which necessitated me having to take a lot of fresh air, get to a pharmacy for medication - usually in a shopping mall - or just plain go home.
You could try Sudoku - put a Chess app on your phone/device - use earphones and listen to Muzak - doodle - walk someone's baby in the pram / stroller [if you're female] - in my late teens back in the 70's when CA's were 2.5 days and ran until 9 pm at night we used to slip away to a corner shop that had a pinball machine and spend some time there. Also at stadium venues we used to volunteer for the overnight "guard" duty of the site and that meant we could go and sleep during the day time session - usually in a camper / caravan - which could be locked from the inside and made to look very unoccupied from the outside.
For these and the 5 day DA's we would volunteer for kitchen duty which could get you away from your seat for entire sessions [they had the program piped into the prep area via speakers] and this also enabled us to meet le femme's as well.