In another thread a poster mentioned that she sees people bringing bread with them when they fly to Hawaii because the price of eggs is so high it saves them money. She rightly wondered if there were other things that people do similarly.
Rather than restrict it to carry on, how about I ask:
Is there anything you take with you when you travel in order to save money at your destination?
Food, spices, clothing, toiletries, electronics?
My wife takes shoe orders from her siblings because the price of quality shoes (like Converse) is double in Thailand what it is in the US.