My wife and I went to Iceland 23-29 SEPT, and it was absolutely magnificent! We can't wait to go back to Iceland, we loved it so much!
We stayed at the Iceland Parliament Hotel and did excursions to Thingvellir, Strokkur, Gullfoss, and a Northern Lights tour; otherwise we stayed in Reykjavik. In Reykjavik we did a food tour, checked out the Settlement Exhibition, the National Museum, and Hallgrimskirkja; and walked all over 101 Reykjavik; and spent a day at Sky Lagoon, including the 7-Step Ritual. All of the meals we had were excellent, including the on-board meals from Icelandair. While in Reykjavik we ate at Grillmarkadurinn, Fiskurfelegid, Loki, Old Iceland, Braud & Co, Baejarins Beztu Pylsur, Apotek, and spent a number of times at Skuli Craft Bar.
Transportation: We had a direct 5.5 hr flight on Icelandair from IAD, it was easy and relaxed, we only do carry-ons when we travel. After arrival to KEF we took FlyBus to BSI. In Reykjavik we walked and took taxis. Returning home we got to KEF approx. 4 hrs before our flight, got through security quickly and waited for the passport control to open at 1330. The boarding process at KEF was a little chaotic, but not too bad.
Practicalities: Never used cash except buying water at the airport so I could get some kronurs for my dad. Otherwise all CC transactions. Make sure you have rain gear and a good coat/gloves/hat. Traffic in Reykjavik can get congested during the week, factor in potential traffic if you plan on going to Sky Lagoon or anywhere outside 101 Reykjavik. There is no tipping, price + taxes are factored into the price. Iceland is costly but worth it, factor the high costs for your trip. Cocktails are very pricey, stick to beer/wine/brennivin shots if you want to drink alcohol and cut down on costs. Icelandic beer is excellent, and brennivin is tasty.
For souvenirs we bought a lot of pictures/art from the various galleries near Laugarvegur and Skolavordustigur. I also bought an Icelandic Bible at Hallgrimskirkja, and an Icelandic-language book on Iceland's history. I started studying Icelandic 6 months prior to our trip, which helped, even though English is widely spoken. Don't be intimidated in learning Icelandic, it's a fun and fascinating language. A lot of Icelanders appreciated an American tourist attempting to learn and communicate in Icelandic. I plan on continuing my Icelandic studies and getting to an advanced level in the language.
Next time we go to Iceland we plan on going up to Akruyeri and visiting Forest Lagoon, the botanical gardens, and Einstok's main brewery, and general exploration around Akruyeri.