My son spd

The noise canceling headphones are a must (i know you have them so thats awesome!). I'd say, if you can, prepare for loud places or things by letting him know and reminding frequently "remember we're going to the fair today and it might get loud and overwhelming so we'll bring your headphones and you can let me know when you need a break". Giving them the words to communicate when they want to leave or need to step away will help tremendously. Im sure you don't but if you're with others, encourage them not to downplay your sons reactions or needs by saying "oh you're fine. Its not that loud". Always affirm their feelings "I know you felt scared when that noise happens. Loud noises can be scary to me too ans it's ok to be scared". I always try to bring fidget things or something that will help distract and calm (whatever that may be for your son) or even just hugging and squeezing while the noises are happening helps my guy too. Hope this helps and feel free to message me anytime! My 6 year old has SPD :)

Try investing in the loop earplugs. They are safe for children as young as 3, easy to use, they come with a little case and he can pick his own color. My daughter has a pair- she refused to wear the regular headphones because they were bulky. I carry the loop earplugs around and she chooses when she needs them, she does a great job too. It makes her feel in control and independent. They reduce the amount of db, but also allow you to talk to them if you need to.

Allowing him to have a favorite stuffed toy with him when feeling overwhelmed, that might help. The thing that I find the hardest is never knowing what is too much for them until it's too late- and they encounter a meltdown or freak out. My daughter does and she'll start hitting both sides of her head, or cover her ears and scream.