You should report your supplies in the Supplies category on the Let's write off some business expenses page.
Type in business expenses in the search box, top right of your screen
Click on first category Jump to business expenses
You will arrive at the
Here's the business info we have so far page
Click Edit
Arrive at the Your Business page
Scroll down to the Business Expenses category
Click start or update next to Other Common Business Expenses category
Arrive at the
Let's write off some business expenses page
Scroll down to the Supplies category