Complete camping accessories are must or you might end up being really uncomfortable. At fairy meadows it is not issue because there are commercial setup of cottages and tents.. so you need not to carry anything..
However, since deosai is a national park, any hotel or commercial activity is not allowed.. At Bara Pani, the wild life scouts rent their own tents for some kharcha pani.. but then again they are very limited and availability is not guaranteed. So if you plan to do camping at Deosai, you must have the camps and their accessories. You need double layer camps (water proof), Underlay mats and sleeping bags.. Blankets don't usually work in this type of environment.