Re: Forfar services mentioned by John Stonebridge earlier, here's my experience from my DIY 400 2 days ago:
I had cause to visit the Forfar Audax Ecosse VIP lounge on my DIY 400 on Sunday. At around 11pm, the McD was 'open' so you could go into the building and avoid the no-bikes drive-thru policy. But it was only open for carry-out, so you had to take your unhappy meal out into the cold and eat it outdoors. They cheerfully told me I was welcome to use the outdoor seating. The petrol station / spar was fine, but the indoor Greggs seating area was all closed off at that time. There was a coffee machine, and next to it, a microwave. There were no microwaveable snacks available to microwave; the shelf was bare. I got a coffee from the machine, a cold sammich from the next shelf, and lurked out-of-sight to drink it indoors.
A minor oasis.