What is the "lunchbox" that other posts talk about replacing?

It's an Air filter produced by K&N that completely replaces the stock airbox.  Part # RU-2970.  Significantly enhances air flow and requires rejetting

So do you buy one or two?
(BTW, I don't buy the part about the air flow being "straightened out".  It is turbulent flow all the way.)
But K&N do flow more air, I have one on my Shadow.  It cost double what a crummy Honda paper filter costs, and the K&N has paid for itself several times already.

You just need one.  It mounts directly to the carbs and has about 2x the filter element area of the regular filters in the airbox.  This allows a much greater air flow than the stock set-up ( much like adding a CAI to a car )  The RU-2970 is actually cheaper than an OEM filter   I got mine for 36 after tax and Suzuki I'm told want's like 45 for a their stock one