9to5Mac posted details on the storage capabilities of the Apple Watch. It will only have 8 GB of storage, and will come with restrictions on how much of that space can be used for different things.
You can store 2 GB of music on your watch, and 75 MB of photos. That's probably only enough space to store a couple of hundreds songs and around 100 photos - not very much at all.
Apple fans might be surprised about the small amount of storage space, although it's likely a deliberate move on the part of the company. Apple wants people to use the watch as a supplement to their iPhones, only storing their favourite tracks and photos on their wrists.
The more expensive models of the Apple Watch don't come with increased storage, either. The steel Apple Watch and gold Apple Watch Edition models also come with the stock 8 GB of storage.