As advice blog Awkward Human explains, when you sign up with the Humane Society, they will ship you a package of address labels for free. You can use these to address boxes, or simply keep them ...

Enter the return address details in the Address box on the Labels tab. Click "Full Page of the Same Label" in the Print section. Click "Options" to open the Labels Options dialog box.

How to Make an Address Label Spread Sheet in Google Docs. The free Google Docs online document service includes a spreadsheet feature that you can use to create a spreadsheet from a data file.