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bringing a good treat/snack in the car... But sometimes he claims he doesn't want to eat when he gets home
Possibly planning to stop and choose a quick snack on the way home... as a transitional activity, a gentle step down from the bustling, energized environment to a quiet home?

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plan for when we get home - for example, I don't want to hear ANYTHING about the evening - because at that point all he can say is the bad stuff
If this is when/how he processes, might journaling help him think things through?

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Netflix, or play a round of cards, or something else that he would look forward to.
These may also be great transition activities, helping him learn to decompress with ease, after a highly stimulating atmosphere.