I'll agree with the other respondents; you're talking data and metadata, which really are for databases.
But, if you're bent on (or limited to) making it work in Excel, the only thing I can think of to do is to logically break up your single sheet into multiple sheets for what would be your data tables if you had them. This could be similar to an ER Model (http://db.grussell.org/section006.html).
So, for variables that change frequently (such as daily sales data), keep them in a main data file sheet. Other variables that don't change frequently, but are part of the main data (like names of sales reps) can go into other files (or other sheets - this is your metadata). This workbook in totum will be your "database." (You're basically creating relationships among multiple flat files - this is actually how the very first databases worked.)
Make sure you keep at least one common field that's a unique identifier between at least 2 sheets (i.e. if you have a sheet for SalesRepData that has SalesRepID and Territory on it, and you have another sheet for TerritoryData that has Territory and CityNames on it, you can then derive sales rep per city between the two sheets onto another sheet).
When you make a report that requires data from multiple sheets (or files), you will then use vlookup and index/match functions to link your sheets.
Finally, for the sake of documentation and audit, which is often overlooked, you should also create a master document that desribes the content of each of the sheets and how each sheet is linked to the other.