Power plugs and prepaid phone cards
Denmark uses the "Type C" power plug commonly used in Europe. You should be aware that in Denmark it is difficult to find a converter that will convert your kind of power plug into the one used here. This is due to some electronics import law. So if you need an adapter, make sure you get it before you leave. More information is available at http://www.kropla.com/electric2.htm
Prepaid phone cards
If you would like to make sure that you can call cheaper within Denmark or have data on your phone for a reasonable price while you are in Copenhagen, you could get a prepaid SIM card. They range from DKK 100 to about DKK 200 to get the card and most of them have minutes included in that price. You do not need a Danish address to get one - you can just go to one of the shops from the companies listed below. There are also a number of online deals, but that may be a little more difficult for foreigners because the physical SIM card needs to be mailed to an address. Your phone will probably need to be free of a SIM lock.
The same carriers as listed above sell limited-time-broadband too. Prices vary, but you can get a limited-time deal for about the same price as the prepaid phone cards.
You can find shops all over Copenhagen. This map includes Amager (the island the venue is on) and the centre.
View Phone shops in Copenhagen in a larger map