It sounds like you have planned your route already, but I'll say it anyway;
Come visit Denmark! In the summer it's great, beaches, partys, culture, nature, history.

When travelling, try to stop at one or more music festivals. There are a lot of them in the summer, and it's one big party with great music!

About the flag on your backpak, defenetly do that. It may sound mean, but often people got this idea of the behaviur of american turists...

Oh, learn to say yes, no, thank you in the countrys language - that always scores some cheap point with the locals.

But other than that, just have fun and meet new people!