My mother in law famously doesn't cook unless forced at gunpoint. So going to her house for dinner usually means that we're going to have some frozen fair or we're going out to eat. Which is fine with me, I'm not there for the food, I'm there for the company. She always makes sure everyone has plenty to eat and drink and all's well.
We're going over there to have Christmas with them tonight and they're going to be going to a luncheon this afternoon before we get there. Fine. MIL called us about an hour ago and said "I didn't have time to go to the store, you guys just go by WalMart on your way here and pick up whatever you want and I'll pay you for it."

Ummmm...okay....
As background, we had not discussed having potluck or anything like that, I was not informed that I might be responsible for dinner. Had I known that I would have bought the neccessary and gone over there this afternoon while they were gone and cooked a decent meal...