It gets very cold the further north you go even in August / September. When you get to Olderfjord (northern Norway) we saw the Northern Lights for 2 nights as the sky was cloud free. If you’ve got an SLR or Mirrorless camera, a tripod is necessary. Shoot at 400 ISO, f/2.8 and about 30 seconds. If you’ve only got a smart phone, there are a number of apps available which most other people were using with mixed results. You’ll need cold, wet and summer clothes for this trip as the weather can be all over the place. Berlin was hot, then as we went further north, it got colder.
Svartisen Glacier trip isn’t mandatory however those who don’t go end up waiting at the boat pick up point with nothing to do. If you go and it’s sunny, no problem. If it’s rainy, care should be taken on the rocks. The glacier is pretty spectacular when you get there after a 3km hike. Care should be taken on the icy part to get under the glacier for that all important selfie and countless likes.
Denmark, Norway, Sweden and Finland are all very expensive, especially alcohol. Alcohol in Sweden and Norway can only be purchased in bulk (Norway I am certain, can’t remember about Sweden or Finland) at Government operated stores. Eating out and everything is expensive in Scandinavia.
Try to do as many of the optional activities, there are a few and they’re pretty great. When you get into Berlin I’d recommend the Fernsehturm. Which is the old comms tower in Berlin. Has a bar and restaurant up top as well as look out. Buy the express ticket at the kiosk outside the main entrance, saves waiting around. Also in Berlin the Hofbrau Haus, a traditional beer drinking hall not far from Wombats in Berlin. I’d recommend a sim card from SIM Corner (I’m certain any country can buy them, I’m an Aussie) but they’re essentially Network 3 from the UK. Worked out to be the cheapest from my perspective. 12GB for $60 AUD I think. Your local national provider may have better options for international roaming.
Some of the accommodation (especially in Olderfjord) is a bit dire. Keep your expectations low in Olderfjord. Most of the places they do a camp site styled dinner setup with a tent and each person is expected to contribute to helping out. Often arriving late in the evening it’s a bit wearisome. Get as much sleep as you can as the drives are horrendously long. Same with lunches, a camp tent setup usually at a petrol station. This is help save travellers from buying extra food.
Again expect cold windy and wet days in Scandinavia. The Nordkapp trip is pretty cool for an experience. We had a very windy and sunny day. If you’re not use to cold, I had about 3 layers. Merrino wool (either light t-shirts or base layers, mid layer and then a wind water-proof breathable hard shell.I have an Arc’teryx Goretex hardshell, it’s worth the investment and quality. Northface does a similar specced without Goretex but similar technology at a lower price.
Merrino socks as cotton stinks when it get wet or sweaty and merrino is anti-bacterial. Wear comfortable shoes, hiking boot are pretty best, but need to broken in first to reduce blisters.
If you’ve got any specific questions, please feel free to ask as I’ve got a lot more info
Remember to enjoy and relax as much as you can.