We packed for early September, weather was amazing, t-shirt and shorts most days. It's a difficult country to pack for, layers and 1 good set of waterproofs and good footwear. Beanie or warm headband, sunglasses.
Really helpful video! We are going for the same time period this year end of Aug/early Sept. Kinda surprised to hear you didn't need the "stiff layers" because I'm hearing that you can't get enough of those! I'm having issues figuring out how many of everything I will need.
I do really feel like it’s a mixed bag! I have friends there right now and they have a thick layer but nothing super crazy. Also look at icelands specific weather website because it’s better than the weather channel and the weather apps!
I wore two at a time! Definitely recommend wind/waterproof pants over layers of leggings if possible. With all the waterfalls and likely high amounts of rain depending on the time of year this will save you time and money trying to dry out the leggings. Hope that helps!