1

Here's a very useful link http://www.layoverguide.com/2011/03/can-i-leave-airport-during-layover.html then look for the Paris section. Both airports have luggage storage.

To help with what you want to see we perhaps need to know a little more about your likes, dislikes and any mobility issues and whether funds are a problem or not.

I'd suggest you also post this on the French section as the locals will give you a lot of good advice.

2

I'd certainly do a hop-on, hop-off tour, and then sit in a cafe and pretend to be Hemingway, or Simone de Beauvoir, and just enjoy being there. The tour will make you want to go again.

3

Leave bags at the airport.

Personally I'd get the train into the centre and then do a 'walking tour'.Much better for me to walk a bit down the Seine and breathe in the Parisian atmosphere rather than try to rush around on a hop-on bus and 'do' things.

The suggestion of a cafe (or a restaurant) for a leisurely lunch is also a good one.....

4

Hire a taxi to take you straight to the Louvre quickly ... And agree to pick you up at that same spot in X number of hours... You can walk to the major sites...rather quickly...get some photos... Actually going into the Louvre...may be a bit much...but it depends on what you want to see...

I'd just go to Shakespeare and Co Bookshop...for a few hours...and call it a day...

5

Hop on / off bus is a good idea (and you could include a run on the hop on / off boat with that) if you'll be coming back and just want a good overview of the town, but you're sitting around 4 metres above the streets surrounded by other visitors and you don't really feel part of the town.

Perhaps better would be a pleasant stroll from (say) Notre Dame, up along the creek past the Louvre to the Place de la Concorde, up the Champs Elysees to the Arc de Triomphe then down the hill to the Eiffel Tower, with detours up interesting looking side streets and a decent lunch somewhere.

If time starts running short you can always pull the pin and head straight back to the airport.