I do my best to predict, based on past experience, what may/may not be a problem for him (too noisy, too many people). I always have snacks with me in case he gets hungry or needs a distraction. I can't count how many times a well planned bag of gummies has saved the sanity of many! My son is now capable of asking for a break, so I will ask him if he needs a break. Often, his body language tells me before I need to ask. If he does have a meltdown, I try to take a deep breath and react calmly. I pull my son aside if it's a busy area or get him to focus on me. "Use your words. What do you want? How do you feel?" Patience and understanding can help manage and prevent meltdowns.

Distractions.
Look Shinny.
Have a Snack.
'Squirrel!'

My wife is very good at watching for my meltdowns. Hey even seem just like child ones.

For me, I can tell when something is about to happen. That is when I either get him out of whatever situation we are in or redirect him with something else. Music works. He usually has his mp3 player with him. I will have him listen to something. I also always carry a new (to him) book. He loves to read. If I can whip out something new for him to read, that can usually stop a tantrum. At home I will have him jump on his mini trampoline or crash into some beanbag chairs. Sometimes, I will just let him scream it out into a pillow. He is usually fine after that. As long as he is trying to muffle the screaming, I don't mind that he does it.

At school, they aren't really able to catch him before he erupts. I know that they will either send him to the hallway to calm down or go to another teacher for some sensory work.

My son has learned that if he's feeling overwhelmed he can remove himself from a situation. He usually just leaves with no explanation--that's when I know he just needs alone time. If the meltdown has already started just let it finish. With my son there is no stopping them. Absolutely nothing will console him or prematurely stop a meltdown.