I also work at McDonald's, but only in kitchen so I can't answer your drive thru questions
I work for a franchise too, so no strike, and I don't know how free food works in normal McDonald's (franchises can have different rules) but we're allowed one medium meal with a medium side and a medium drink for our break. That's not a lot to sustain you when you're on your feet for eight hours doing heavy lifting (and when you're short like me, also being constantly on your tiptoes because they design McDonald's kitchens for the height of the average man), so that's how McDonald's workers can be slim.
Sometimes we get your oder wrong (ketchup instead of brown sauce, cheese on a double hamburger) because we get a LOT of orders. I can dress a double cheeseburger in a few seconds (squirt ketchup and mustard at the same time, onion on as I pass it on the line, grab two pieces of cheese and two pickles with ones hand, place in one motion). The major of burgers we make are some form of cheeseburger. Over 90% of beefburgers are cheeseburgers. When you make that many cheeseburgers, you can do it on your sleep. You just zone out and start doing it by pure muscle memory. So when some orders a hamburger, I usually put cheese on it and push it down the line without thinking, then have the hurriedly pull it back and rip the cheese off. Sometimes I don't notice I've put cheese on, and the person putting meat on will have to point it out to me. Sometimes we're both so used to the constant cheese neither of us will notice, and the customer gets the wrong order. I feel your pain though, I absolutely detest cheese.
With ketchup v. brown sauce, its likely it got handed out wrong. The wrappers are very similar, and the brown and red look very similar too. They should switch the design up to make it more obvious imo. Just ask for a new one though, they won't mind too much.
About getting shitty nuggets... they haven't been reheated fifty times, they get cooked in advance abd then stored in a heated container till they're ordered. If you go when it's quiet, you'll be waiting a while. Ask for fresh if you want, but I'll warn you they taste three and a half minutes to cook (customers have asked us for fresh food before, then complained its taken too long. You can't have it both ways mate.)
Veggie goujons and fries are made together on the opposite side of the kitchen to the meat. But the veggie wraps and burgers are made on the same assembly line as the meat products. Yes, my hands that have touched the last person's big mac WILL wrap your veggie wrap straight after.
One request to all you customers - DON'T ask for saltless fries if you want fresh, JUST ASK FOR FRESH, PLEASE! It's way too much effort to have to try and clean all traces of salt from a section of the fry station.