Blue lagoon

Unless you want extra spa treatments, getting the most basic package will do the trick. Only you know what you want to pay for (basic access into the pool was just fine for me - it was already expensive enough). As far as killing time, it won't take you anywhere close to 2.5 hours to get your bags, car and then head there. It's a tiny and efficient airport without many flights coming in at the same time. I don't remember how far the drive to the lagoon is from the airport but there should be no cars or traffic to worry about. Maybe you can take some time and eat breakfast at the airport first? Otherwise you may be sitting a the gate of the Blue Lagoon for some time. Perhaps a better alternative you may want to consider is hitting the Blue Lagoon right before you leave Iceland as opposed to when you come in. That would probably be a better use of your time if you're trying to cram a lot of stuff in. That way you can hit the road right away and maximize your time.

We were in Iceland for 3 days last summer. Our flight also arrived at 6:30 and I believe we were on the road by 7:15. If the weather is good you could do the golden circle tour and head back to Reykjavik afterward to see city sights and have dinner. If the weather is so bad you want to stay indoors you could spend the day in Reykjavik and visit museums. Either way save the blue lagoon for the evening to unwind at the end of a long day. We did the standard which cost 40 euros and spent about an hour in the water.

Thanks for the help! So based on the suggestions, it is not going to take as long to get out of the airport so our plan will be:
1) Land at 6:30am
2) Rent our car at blue rental car
3) Checkin to our bed and breakfast (located right by the airport)--that way we can drop our bags off
4) Drive the Golden Circle Route
5) Then on the way back to the bed and breakfast near the airport we still at the Blue Lagoon

Does that sounds like a good plan?

Any thoughts on places to eat along the way of the Golden Circle Route? And the Blue Lagoon closes at 9pm, what time would you suggest we get there in order to allow enough time to enjoy it? Is it busy late at night like that?

There was a decent restaurant at Gulfoss Falls. There was also one at Geysir, but we did not visit it so I can't vouch for it. There is a small coffee/snack place near the turn off for Pingvillar. Those are the places we stopped when we drove the Golden Circle last September.

Your itinerary is quite doable. Consider a drive through of Reykjavik if you have the time, but that would require doubling back. There might be things to see of more interest to you driving a more direct route from Gulfoss to the Blue Lagoon.

For a quick drive through of Reykjavik I would recommend stopping at 1) the sun voyager statue, 2) Harpa building, 3) the hot dog stand where Bill Clinton ate (get it with everything on it), 4) Tjornin Lake and 5) Hallgrimskirkja (go to the top for panoramic views of the city if it's open). There is so much more to see and do but you could do this drive through in less than an hour if parking and traffic isn't an issue.

Also, there was a flashpot on 36 shortly after leaving the ring road on our way to Thingvellir so watch your speed. We also ate at the Geysir cafeteria which was fine and quick. Bring snacks and drinks with you to save time on the road.

If you’re still planning a visit to the Blue Lagoon, you might be interested in knowing that you don’t have to pay anything to park and walk around the lagoon, checking it out as you stroll. It’s only if you decide to purchase a spa package that you have to pay. Also, it’s important to know that the lagoon is not a natural feature…all of that funky-colored, hot water is actually the by-product from a geothermal power plant. It’s piped in. Sort of a let-down, but it still looks nice.