God no, please don't be that woman. Don't run around procuring food, don't kill yourself cooking at the very last minute, just don't. Go out, go to your friends, family, hotel, anywhere.
My parents have the exact same dynamic. Dad springs things on mum hours before the thing/event, sometimes she even opens the door to see inlaws/relatives already standing there with no warning. She rages when they leave and says 'never again'. Until the next time. Has been going on for decades.
My ex tried to pull this once. Phoned me at lunch break to 'chat' and at the end of convo casually announced his friends are coming over later that day, and could I sort out some drinks/snacks. Could I fuck. I came back, changed, did my makeup and went out with my pals. I did warn him I'm not doing anything for him, he just didn't believe me. Dickhead was left with hangry friends and empty table. He didn't do it again, though.
Ah yes, please don't involve your MIL. That would be two women solving grown ass man's problems. It's pathetic. He's an adult, he can sort himself out, ADHD or no ADHD.