How can I add an item to a sale using a Custom POS button?

If you have a common item you'd like to ring in by clicking on a button, you can do so by using Custom POS Buttons.
First you'll need the Item ID of the item you want to create a button for.
Run Store Operations Administrator, File, Connect, enter the SQL password, and click OK.
Select Database, Query and enter the following.

SELECT ID FROM Item WHERE ItemLookupCode = 'xxx'

Subsitute the correct item lookup code for xxx.

Press F5 or green arrow icon to run the query. Note the ID shown.

Run Store Operations Manager and select Database , Registers, Custom POS Buttons, New.
Number: next available number or open spot (0-9 are top 10 positions)
Style: Internal Command
Caption: Short description of button
Command: PerformAddItem x1, x2, x3, x4, x5, x6, x7
(notice the spaces after each comma)
x1 = Item ID
x2 = Item Lookup Code
x3 = Quantity
x4 = Override Price (0 = No, 1 = Yes)
x5 = Price (0 = use price on file)
x5 = Override Description (0 = No, 1 = Yes)
x7 = Description (0 = use description on file)

Example: PerformAddItem 1, 1000001, 1, 0, 0, 0, 0
This would sell Item ID =1, Item Lookup Code = 1000001, Qty =1, at current price and description

If custom POS are not already displayed in POS, press Ctrl-F6, Transaction Screen tab, and enable "Display custom buttons on the right".

IMPORTANT: If you have several items you want to do this with and are running Feature Pack 2 (2.0.1000) or higher, you should use POS Task Pads for this function instead. POS Task Pads replaces custom POS buttons with expanded functions such as color coded linked menus with F-keys and common functions available on the task pad. POS task pads are best deployed with a touchscreen monitor. Task pads can include any previously defined custom POS buttons.