The fact that firefighters go out to get groceries surprises anyone? I'm pretty sure that every firefighter movie has a grocery store scene.
If the issue is being out of their district, I agree with those who said that I'd rather they be out of their district and close to quarters, rather than in their district and far away.
My town is over 100 square miles. And surprisingly, other than a huge number of Chinese and Pizza joints, there isn't much to eat at night. If there are multiple crews on, nobody objects to going two minutes over the town line to get food to bring back. If a call drops, the other crew can cover (while the rig on the food run heads directly back to town in the event of a second call), or you're actually closer to the most populated part of town than you would be in quarters.
I think this is making a mountain out of a molehill. I don't begrudge the FFs dinner, and it's safer for all concerned if they stay together, which means using their apparatus to travel to the store.