Monitor your own stress level and know your triggers so you can mitigate them. Have a plan for when mitigation fails.
I find that my stress levels peak (and I am much more likely to meltdown) when I am BOTH hungry and frustrated. So I mitigate what I can by keeping an apple at my desk to stave off hunger and getting enough sleep and excercise to stave off frustration.
Both excercise and the apple work for me on multiple levels. Excercise vents my frustration and helps me learn to regulate my breathing and heart rate, both of which are good skills to have when a meltdown is coming. The apple gives me a 3 minute breather where I am distracted by the task of eating and that often takes my head away from whatever is frustrating me at the moment as well as taking away the hunger fight or flight state.
When I feel overwhelmed and a meltdown is imminent, I look for a physical outlet that cannot cause harm. I like to try to dent my heavy bag or put miles on my running shoes. I find that not only is this useful to vent a meltdown in progress, but if I excercise on a regular basis, I sleep better, feel better about myself and am less likely to get frustrated by venting on a regular basis.
Meltdowns are like volcanoes. Eventually the volcano will erupt. If the volcano erupts a little every day, we can harness the energy in a positive manner. If a volcano caps itself and builds pressure, it will eventually explode taking everything around it.
In short:
1. Know your triggers and mitigate them.
2. Have a plan to get out of frustrating situations.
3. Avoid situations that allow you no way out.
4. Do not abuse your plan. Don't allow others to see your condition as an excuse.
5. Mitigations that do not allow you to vent are not cures. Eventually the apple is not enough and I will need to vent. Normal excercise vents me daily and keeps the apple relevant.