Ditto on the ATMs. In 2000 I went all across Europe using mostly my ATM card, and had no problem other than having to figure out how much local currency to take out. But watch those overseas ATM fees!
Sunspace’s little bag of travel tricks:
If you are going to be in one country for the whole time, get an unlocked GSM mobile phone and use a local SIM card (which gives you a local number). Avoid paying those freaking expensive roaming rates. You may be able to get your existing GSM phone unlocked, if you already have one.
Send text messages for simple inquiries (“Are you at our meeting point yet?”). Cheaper than roaming calls, and quieter too. Of course, this assumes that your companion has a mobile phone as well.
If you want to be on the bleeding edge telephonically, get a Skype account with SkypeIn and SkypeOut capability, buy a WiFi-enabled Skype phone, and make all your calls across the internet from WiFi hotspots for pennies a minute.
Stay in youth hostels. Despite the name, you don’t have to be a youth to use them; in most cases they accept travelers of any age. I have a lifetime membership in the IYHF, but there are other organizations of hostels. Often they have the word Backpacker in their names.
Join Pasporta Servo or another hospitality exchange and stay for free. (Meals generally not included.) I stayed in Copenhagen for three days this way.
Buy simple food at grocery stores and prepare it yourself rather than always going for fast food or restaurants. If you stay at a hostel, there is often a kitchen area for the guests to use. You may need to bring your own pots, dishes, cutlery, etc.