Make sure there is loads of straw round it, this will ensure good insulation. Are there any other rabbits? If so, keep them close together. Also, depending on the temperature where ever you are in the world, you may want to take the hutch inside. Blankets are always good, but could suffocate the poor thing. Is it a newborn? Like was it born from one of your rabbits at your home? If so, I think you should really try hard to keep it warm, but if it doesn't survive then that is just fate. Survival of the fittest.