After completing the Dark Brotherhood (Assassin's Guild) quest line you are given a special horse. It is the fastest horse in the game and has the added benefit of being unkillable because it is a unique character. That's where the cheat comes in. After obtaining that horse, attack it until it falls uconcious, then loot it to enter its inventory. You can place whatever you want in its inventory, and after a few moments, it will wake up and you can ride it again just like normal. When you want to access your items again, just beat the horse unconcious again and take what you want. This way you can easily keep and use all your items without constantly having to return to your home or weighing yourself down.
