Linda
Go for layers you can put on take off, When I went it has January and the weather was good, we did get some downpours, also I wanted to do many of the extra flights but due to weather conditions I only managed the helicopter flight to the Franz Joseph snow on the top when we got off, so you would need something warm for that.
There are many hotels that have washing machine but bear in mind you won't be the only person who wants to do a wash, so mack sure that's at the top of your case, and get in quick, if not pack a tube of travel wash for the smalls!!! Lack as if your going away for say 10 days..
See and do all you can its a very long way to go so make the most of it.
Take things for the plane journey music, or if you have ipad then download some films etc, books etc..
make sure you have comfy clothes and shoes as many hours are spent in planes or coaches etc.
Cindy