Why Not! Souvlaki in Firostefani was our favourite place for a quick and tasty gyros lunch, and I can also recommend Meat Corner in Fira.
Mama Thira is the place to go for souvlaki - I had it there twice and it was beautifully tasty both times - and I had the best fava at Rastoni (Fira). It came with smoked almonds and roast Apaki pork, though I'd give Rastoni a miss and have tasty fava from Pirouni (Firostefani) instead. Pirouni offers massive portions - you could quite easily share a main, even if you're super greedy - a great view of the sunset, plus the staff were lovely. Aktaion is another nice little Firostefani restaurant. As for Fira, try Naoussa - their pork in Santorini sauce was so yummy. We also ate at Vanilia (Firostefani) and Fanari (Fira), which were nice enough.
Two courses each, a bottle of wine and water at most restaurants costs between €65-100, and you usually get given a free dessert or shot. We found that the restaurants in Fira are slightly more expensive than Firostefani, and slightly less tasty. If you want to have cocktails in Fira, we liked V Lounge.
Artemis Karamolegos Winery, where you'll also find the #1 rated restaurant in all of Santorini (as voted on TripAdvisor in September 2015): Aroma Avlis. Although we didn't have a tour, we did do a wine tasting session and tried six different glasses of their wine for €8 each. Our favourite was the Nykteri, though I really liked the dessert wine: Vinsanto.
Another popular drink on the island is Yellow Donkey (the Santorini Brewing Company also do Red Donkey and Crazy Donkey), which Olly loved. As for Aroma Avlis, the food was delicious and ridiculously cheap - definitely get the Santorini sausage starter - and I'd highly recommend that you visit both the winery and the restaurant.
As for what else you can do in Santorini if you're not feeling lazy like we were - lots! One option is to rent a scooter, quad bike or hire car to take yourself off around the island, as taking taxis all the time will get quite expensive. For reference, a taxi from the airport to Firostefani will cost €20-25, and that's only a distance of 3 miles. Another option is using the local buses, which we used to get to Oia and back.
- The Prophet Elias Monastery - the highest point on Santorini
- Akrotiri - the Minoan settlement preserved by the volcanic eruption 3,500 years ago
- Mesa Gonia - a village that was deserted after the earthquake in 1956