I was lucky enough to be visiting close friends of my family when I was traveling around this summer, so I haven't really had to deal with finding places to sleep. One thing that we did to cut cost that I think was mentioned was hit the local delis and groceries. My friends are Vietnamese, so I definitely have a VERY different experience of Paris than I would have if I went strictly as a tourist.
Trains are a must!!! If you can navigate the trains in Paris, you'll survive anywhere!
If you're planning to travel to Italy, one trip you've gotta take is a drive along the Eastern coastline. There's about a nine hour stretch from Milan to some of the major cities further south, and I could have sworn I was in the Carribean with the deep blue green that I was seeing in the water.
As someone else said, Passports and copies are a must!!! ESPECIALLY in France, I found.