As the summer is my favorite time of the year and that the beach is just 15 min bikeride away, I recommend Amager strand. Full of people usually though, but even so it gives a bit of an exotic touch to such a scandinavian city with the sea and the bright sand in the hot summer days.
Super easy, healthy and affordable lunch and dinner takeaway. As a tourist in Copenhagen it is a nightmare to find affordable food. The popular downtown areas are flooded with crap food tourist traps and it's hard to navigate through the bullshit. Smag means "taste" in Danish and their ryebread sandwich with salmon, green pea puree and peanuts is a treat.
Assistens Cemetery is one of the only cemeteries in the center of Copenhagen and beside from being a beautiful calm place to hang out, sunbathing and having a picnic, it is the final resting place for many great people through times. H.C Andersen, Søren Kirkegaard, Niels Bohr, Henry Heerup is just a few of them.