I was there from 97 to 2000. Loved every minute of it.
I was stationed on a military base so it was no problem for me to interact with other people who spoke English. I can't remember if there were any Dunkin Donuts in Okinawa but there were McDonald's, KFC, and A&W. The A&Ws over there were like the Sonics you see here in Tennessee. There was also a Japanese fast food chain called Mos Burger. There was also a Shakey's Pizza. As far as restaurant chains went my favorites were Hokka Hokka Tei and Coco Ichibanya. There were several great local restaurants there as well.
Okinawa was also the first place I had taco rice and Japanese curry. I still make both sometimes. There are a few restaurants in Knoxville that serve Japanese curry.