Weather is similar to our Summer, but be prepared for anything! The saying goes that if you don't like weather, just wait 15 minutes... You can only take 3Kg of food each into Iceland. I got fined for taking 26Kg between 2 of us as I forgot the limit...
Comprehensive tool kit.
Decent camera and video camera to capture your memories. I made a movie of my trip and it is really magic to remember the fun you had there.
Decent all terrain tyres.
A mate with another vehicle to go with you should the worse happen, or meet up with some locals such as this lot.
www.islandrover.com.
Camping is plentiful, there are lots of sites dotted about. Cost about £7-£8 per night per person.
Camping in the interior is ace, but be prepared for it to get a bit fresh at night...
Something to do on the ferry. It is a 31 hour crossing. don't forget to take your sleeping bag from the car as you cannot return to the car deck once you leave your vehicle. Ilearned the hard way and got very cold. Ear plugs aren't a bad idea as it isn't exactly quiet onboard!
I can't wait to go again...
Si