Adding new sales and expense options

Is it possible to add categories to the existing sales or expenses options? I would like to add the sales categories we have on our receipts (in a restaurant) to get a quick overview of how much we make on certain items. The same goes for the expenses; I need to know how much we spend on certain items. Is this possible?

Do you mean being able to add new income & expense accounts? If so, you need to go to Settings tab, then Chart of Accounts.