Shipping carton Allocation?

I have an interesting dilemma. I have a table with column A as store number and columns B through whatever as part numbers. The intersection is the number of a particular part ordered by a particular store....typical. So each row is a shipment. We just got a new requirement from the warehouse that WE now need to determine which parts go in which carton per store. A carton can hold a max of 30 items.

I am an old dBase programmer, so the pseudo seems straight forward 'total=total+item....if total >30 then total=item-(total-max)...etc'. Essentially I need to add quantities for carton 1 until it equals or exceeds 30, then increment the carton number by 1 etc.

Anyone have an approach in Excel that might work?

Thanks