I am a public speaker with Asperger's syndrome and the question I get asked more than anything else is how to end a meltdown. I don't have an answer. I go through them and I don't know how to cut them off. All I can do in the middle of one is chose to walk away and be alone rather than emote in front of others. And getting there took maturity and lots of past mistakes. I firmly believe that the best remedy is to be self aware and live a calmer life. I made a chart for myself, I call it the Stress Chart. It helps me to be mindful about my daily experiences and how they effect me. If you want to see this let me know.
Another thing people talk about is having an emergency sensory kit. This might include a bag with a music device and head phones, some aroma therapy, something that is texturally pleasing. I wear a perfume that relaxes me and wear my winter hat with ear covers, usually while I have flip flops on my feet. My feet need to breath and my ears need to be protected but hey, it helps.