Also in case it's any help, we did this last Wednesday (my husband and daughter's first visits to Paris so just to see the main sights really) ...
RER to Charles de Gaulle Etoile (takes about 45 minutes as it's right over the other side of Paris).
Got off at C-D-G Etoile to see Arc de Triomphe
Walked Champs-Elysees as daughter wanted to go to the
Disney Store!
Walked Ave. Franklin D Roosevelt towards the river
Lunch in cafe by the river
Walked to Eiffel Tower and went up to second floor
Played in fountains at the Trocadero! (it ws VERY hot)
Got boat to Notre Dame - this wasn't the most cost-effective thing to do as it turned out you have to buy a day pass for the 'batobus' (water taxi) but we'd promised my daughter a boat trip and I don't really do boats - certainly not long enough to do a whole round trip! It would have been a lot cheaper to hop on a bus or the metro!
Had a look round Notre Dame
Walked to Hotel-de-Ville
Took metro to Nation then changed to RER for the journey back