In reply to Panick:
With our old Weimeraner Dave, god bless him, we used to put ruffwear boots on him and a lined goretex jacket.
We took him up Snowdon one November and he really suffered so bought him this kit and he was toasty. I found that the cold and ice used to really play havoc with his paws so bought him the boots.
Initially I thought it was overkill but on top of the Ben one day, we met some MR guys with their dogs and they had the same sort of set up. He hated having the boots put on but soon learned to love them :0)
I also took him on a few overnighters with me and the jacket had attachments for panniers and he used to carry his own food and water for the day!