Paul,
Having been to many Greek resorts (island and mainland) I don't believe the inclusion of chips is by any means universal. I would say little more than 50%. The other normal ingredients for a gyros pitta are the gyros meat (obviously) which I believe is lamb, onions, tomato, and plenty of tzatziki. If chips are present then this cuts down on the meat content.
The largest I have had were found at Tingaki (Kos) this year- I believe the place was called Memories. One sufficed for my partner Diane and two for me. In many places I can manage three. They go very well with very cold retsina (or Greek beer).
I loved your pictures of the gyros pitta. Maybe one of the regular visitors can inform me how many places in Plakias are selling them currently. I remember a small place on the seafront near the harbour, run by a lady, but this was several years ago.
Mike