Paris: Go to the Moulin Rouge Strip. Its in the Montemart area. Major partying with dozens and dozens of clubs on this one road with the Moulin Rouge. The partying goes on till sun rise. If you try a crepe then make sure you dont buy it near a toursit site. You can save money and buy better ones away from an attraction site.
Rome:"Gillati" icecreams are all relitivly the same price anywhere in the city. If you are going to to get on and your on a budget then the best thing to do is just buy from the place that looks best to you.
Stay at the top rated hostel on HostelWorld.com or hostel.com, the Tpunk hostel search uses those sites. Make sure it has a bar. The bar acts as a common room and makes it so much easier for you to meet people, especially since you will be traveling alone.
Shop around when yu get to your destination, find the cheap places to buy the same items ie: water, food, souvenirs. In most palces you can buy a liter of water for one euro right outside the trainsation or where ever. But if you walk two blocks behind it you will be able to buy the smae thing for 25 cents.
Have fun and remember to enjoy your travels. Good Luck! Best of wishes from the Tpunk community!