I use Excel as well. I keep separate sheets in a single file for all the different types of expenses and profit that you can include on your Schedule C (if you're in the US) at tax time, such as:
-Supplies for resale (in my case, things like paper, mats, frames, etc.)
-Total Income from sales (including what the buyer paid for shipping)
-Shipping costs for Items sold
-Equipment/supplies for the business (not for resale)
-Fees (e.g. Etsy and Paypal fees)
-Memberships
-Continuing Education
-Advertising
-Mileage
-Home office expenses (e.g. percentage of rent, utilities, etc. used for your home office)