Europe Packing Checklist
You might not want to bring everything on this list, or you might want to bring more. But this gives a good idea of the essentials of what to pack for Europe. Decide what you really need, if you can get away without it you'll probably be glad you didn't bring it. I tend to under-pack and traveled for 6 weeks without a sweater, until I hit Switzerland and had to buy one. Most of what you need you can buy there so there's no reason to panic if you forget something (except the passport!!) but its nice to have the basics covered.
Keep Planning Your Backpacking Trip
Choosing a Backpack or Luggage