MAN T3 would generally refuse to accept the booster seats made from polystyrene and weighing around 2kg (the heavier metal based ones were fine).
Oversized were picky with anything below 5kg (they could stick the item in a tray, but preferred things directly on the belt). Something to do with the item getting stuck in the belt if too light.

A suitcase full of crisps ought to be fine. The suitcase itself would weigh a few kg and provide protection.