How do you predict a continuous variable when all your independent variables are categorical
It depends on the problem statement, have you got some background about the source of this dataset.. if not then predicting sales in the most common type of analysis you can do here.

And regression doesn't really only depend on input values, it is also considering the past output values so do not worry if the input values are all categorical. You can also try gradient boosting regression trees for predicting sales in partner stores.

Aprt from predictive models, its also a good idea to do some data analysis and  find trends and patterns within your data by utilizing graphs