If you have 5 days in Iceland you have to go see the south coast. It's the most spectacular area of Iceland. You will se the majestic waterfalls, black beaches, green canyons and vast glaciers of Vatnajökull.
Tours
There's 5 tours included in this itinerary, Katla Ice Cave, Kayaking with Icebergs, Glaceir hike, Horseback Riding and Whale Watching. You won't be able to do all of the, so pick your favourites. Remember to book in advance as they do sell out. Use code "ASASTEINARS" for 10% discount.
Local Pools
When driving around Iceland a great trick is to use the local pools. Almost every little town has one and they are like a mini spa. Always with hot tubs and always outside. Entry is $5-10 so it's very affordable to hop in for a quick dip in the jacuzzi. I use them all the time when travelling.
Campsites
There's plenty of campsites to choose from in Iceland. Here I have recommended my favourite ones. You don't need to reserve in advance and can just show up. I would also recommend to not buy the camping card as most of the campsites I recommend here are not included.
Supermarkets
You will pass a supermarket almost every day along the circle. The only section with less services is between Vik and Höfn. If you stock up for 2 days at the time you will be all fine on food.
Good luck and enjoy your trip in Iceland!