When you arrive at CDG airport in Paris, how do you get into the city?

Oskar prefers to take the RER which is easy for him as he travels light... one small bag and he is ready to go.  The price is good at 9,10€ allé simple (one way) and there are multiple options for stations and transfers after you get into the city.  Be sure to hold onto your ticket as you will need it to exit any of the arrival stations.  On my last trip into Paris with Oskar and Holly, we departed the RER B at Châtelet les Halles to walk several blocks to our apartment.  Now, let me say that Châtelet les Halles is an enormous arrival station with many levels.  We were simply headed for the exit at street level and did not have to take the stairs even once.  We rode at least 5 escalators but no stairs either up or down. 
Note: This does not work going the other direction!

Another option from CDG is the RoissyBus which leaves every 15 minutes from Terminals 1, 2, and 3 and arrives at Opéra (Rue Scribe and Rue Auber) for 10€ one way.  You do get a more scenic view for your arrival in Paris and you do not have to be worried about the dreaded stairs.  The return is just as simple with the departure from Opéra every 15 minutes.

If you are not concerned about the cost, you can simply take a taxi, but I can envision all the other ways to spend my Euros and with only carry-on luggage it is not that difficult to avoid a taxi.  If you go to the links above you can plan for your arrival and transportation, deciding on the best option for your preferences and final destination in Paris.

Oskar says, "Bienvenue à Paris!"