Badger Girl Goes to the Continent

Ashley and I bought are tickets today. Europe, here we come! Well, actually on September 2: Paris, here we come!
We leave LA on September 2 and come back on September 18.
So far, we plan to fly in to Paris and meet Rebecca in Rome on September 7. We'll spend the next week in Italy and then head back to Paris to fly out.
So, I would like to begin soliciting for the following bits of advice:

-Ways to save money traveling, eating, and staying
-Places to stop on the way from Paris to Rome AND in Italy
-Things to do in Paris and Rome that don't cost very much money
-What type of luggage to take
-Any other pieces of advice