Carry warm clothes with you. Since it's almost cold all the time. Always apply creams and balms since your skin will dry quickly. Carry Cold tablets with you, since you can catch cold so easily bcoz of winter.
Travelling to manali and just visiting mall road and all is what all people do , to do something different and to make the memorable trip one should visit old manali instead of new manali ,old manali is comparitively less crowded and full of beautiful cafes located beside the beautiful beas river.
Always try to use local transport . when you use cab services then its always give you extra weight to your pocket & when you use local transport for traveling they gives you extra open environment for travels.
Spiti is a lovely place and makes you feel on some another planet. I visited spiti last year and here is every bit of detail, you may need. This includes all my personal experience from complete itinerary of 7 days, a road trip Manali to Spiti