Cardboard is the only thing in this trade we can pass on rather than pay to dispose of, so on a shop round it does not count against the daily allowance at all, provided it is flattened and dry.
Flattened matters because a truck fills with air otherwise and a round that should take three hours takes five. Dry matters because wet cardboard is worth nothing to anybody and goes to disposal with everything else.
Several shops now keep a corner for it and their monthly figure dropped a band as a result. We will come and look at a stockroom and say honestly whether that is worth doing for you.