There are three ways to pull a CSV file with all of your stock items depending on your needs:
1. Whether you have access to an FTP/SFTP or a Dropbox account, you can set up an export in Settings > Export Data > Export type: Inventory.
Full details on the specifics, selection criteria, available columns and available filters are listed here.
2. To download a CSV of your inventory locally, you can use the My Inventory Export feature. Full details on using this tool together with the available options are given here.
3. For very specific reports on Inventory, which can be downloaded locally as CSVs, you can use Dashboards > Query Data tool, which offers an array of reports related to inventory items.
For just a list of SKUs in your My Inventory, you can use either Query type:
Full list of inventory-related reports available in Query Data is visible here.