You can export accounts, contacts and opportunities by clicking the 3 dot menu on each page:
The Excel or CSV file will contain an export of all related data. Just delete the columns you don't need.
Excel: split text into columns
Exporting to CSV and don't have columns right away when opening in Excel? That sometimes happens, as some language versions of Excel expect commas and others expect semicolons.
Then use "Text to columns".
... and then "Comma".