well...here's a thought....just my opinion....
I would let both husband and son know who has the only set of keys and inform them that your son's equipment is in the car. Then say you know what you need to do if you want your equipment for tonight. (Write the mechanics number on a post-it) Stick the post-it to the fridge and say "here's the number to get your keys. Mommy is going out to take care of a few things for herself." go get yourself a manicure and pedicure or go shopping but turn off the cellphone.