Thanks for your reply.
If you're simply looking to kill some time in Paris, and see a few sights, I'll mention that St-Michel Notre Dame station (where you've got to change trains anyway) is right by Notre Dame Cathedral and also a convenient access point for the Latin Quarter, which is packed with cheap (but good) restaurants. A decent three course lunch costs from about €12 to €15 in many places.
If time permits, an alternative way to get from St-Michel Notre Dame station to the Eiffel Tower is by using the frequent Batobus river services, which operate from close to the cathedral. They take about an hour for the journey (instead of a few minutes on the train) but you get some lovely views of Paris along the way:
http://www.batobus.com/english/