One of the golden rules in sales is that if you are providing a discount you must take credit and clearly articulate that discount. To achieve this the following fields are are required or the ability to calculate and display. In addition to item categories on an estimate.

Columns - Should be able to display in any order
Item #, Item SKU, Item Name, Item description, Qty, List Price, Extended List Price, Discount %, Discount $, Extended Amount (Total)

I have see reference to "Groups" and "Chapters". This requires and item level field to be able to "bucket" items into defined categories. Example would be Hardware/Software, Service, Annual Maintenance.