I used to cry at work a LOT. I was constantly running to the restroom to let it out a bit to see if it would help. Sometimes it did, sometimes it didn't.
While walking to the restroom I tried to use a grounding technique I'd heard of that is focusing on the sole of your foot with each step, feeling your heel make contact first, then ending with your toes.
I also wrote notes for myself. I journal but of course can't journal at work, but I could write down important things--feelings and the thoughts associated with the feelings. I would keep add to it as the day went on. At some point I would tuck it into my purse to take home to think and write more about later.