What was the purpose of your trip?
How long were you here/there (or gone) for?
Who were you travelling with?
Where did you meet ____ [person mentioned earlier]?
Who packed your bags?
Did anyone give you anything to carry?
Did anyone help you to pack your bags?
Where have your bags been since you packed them?
How did you get to the airport?
How long did it take to get to the airport?
Where did you stay in ____ [place]?
What was the address?
Do you have a receipt/bill for ____ [hotel stay, cabs, restaurants, etc.]?
Do you have any electronics in your bags?
Have any electronic items you have been repaired recently?
What's the name of ____ [person mentioned by passenger earlier in the conversation]?
What's the last name of ___ [person mentioned by passenger earlier in the conversation]?
Can I see your itinerary?
Can I see your ticket receipt?
Who paid for your ticket?
Why did you fly from ___ [place]?
Where do you live?
What do you do?
What is the name of your employer?
Can I see your business card?
Can I see your frequent flyer card [for this airline]?

Any other questions you've been asked or observed being asked?