You can browse your data, using a complete list of all products the data source contains.
It’s possible to filter out those of the source’s products which aren’t being used by any campaign (1.). You can also use the search function (2.).
Previews of individual values is one way for you to have a good general overview. All you need to do is click the magnifying glass next to the name of the variable, and a window pops up, showing the information about that variable’s products.
You can find more information about variable previews on our blog.