Oh, I forgot to mention one thing. We are two guys from Brazil, so we might not have the proper equipment for close to freezing temperatures. So, if you could suggest anything we should buy before trekking or doing any other activities you suggest it would be great.
Well, if you can't carry any camping equipement, I really recommand you rent a car. Some companies can arrange delivering in Seydisfjordur and leaving it in Keflavik for example. Or you can start by bus to Egilsstaðir, and rent a car there. or in Höfn if you want to rent fewer days.
A great place to stop for 2-3 days is Skaftafell, but there is only camping where the bus stops, so if you can't camp, rent a car so that you can stay in surrounding hostels or other sleeping bag accommodation, and get to Skaftafell during the day to hike. There you can hike on your own on marked trails, or you can buy mountain bike trips, or glacier hikes, from a company called www.mountainguides.is or www.glacierguides.is
The Mountain Guides company also offers some grat hikes from Skógar area. Look for Fimmvordurháls and Eyjafjallajokull trips. If there is a trip going to Thorsmörk, that's great as well.
I'd recommand you go through an agency if you do an overnight trip. They will send you a detailed equipement list. But definitly consider waterproof sturdy cloths, and hiking boots, gloves and hats, warm sweaters and fleece jackets, avoid cotton clothing which keeps humidity and cold and prefer whool, or synthetic fabrics.
Don't hesitate if you have more precice questions.
Thank you so much for all the info, Myriam! You made me consider bringing a camping tent to Skaftafell(unless one of the companies that organize trekking or mountain biking expeditions can rent a tent)!
Besides Skaftafell (and Maybe the Skógar area), I was thinking about visiting Jökulsárlón, Gullfoss and, of course, Reykjavik. Do you think 7 days is enough to visit all these places? If not, which place do you think could be left over during the trip?
Thank you one more time!
One of the most helpful things I've ever read!