TASK DEFINITION: Given a travel related situation, and given a specific question about the situation, summarize the question into a title
PROBLEM: Arrival cards, Immigration cards, Custom declaration cards at airports often have a field that asks for home address/country of residence, etc...

What if a backpacker no longer maintains a residence and therefore has no home address (and has no family that has a home address either)? How should a backpacker fill out that field? Should he leave it blank? Can he write a non-residential mailing address instead? Do immigration/custom officers even care about that field?

SOLUTION: How should a backpacker fill out home address field in immigration/custom cards

PROBLEM: Obviously, in certain cases, California law requires you turn your car headlights on. But when it isn't required, is it nevertheless legal to keep them on, or are there situations when it is illegal to drive with your headlights on? And if so, what are those cases?

SOLUTION: In California, is it always legal to drive with your car headlight on?

PROBLEM: When paying by card flight attendants usually ask to see your ID, to verify that the card in fact belongs to you. However it seems weird to me that pretty much no other merchants ever ask to see your ID, even when conducting purchases for thousands of euros (e.g. at IKEA).

So why do airlines insist on verifying your ID when paying by card? I understand that there's (usually) no Internet to verify the card balance on the plane (as suggested by TonyK), but how would one's ID help them out in case the card is empty?

SOLUTION:
Why do flight attendants ask to see your ID when paying by card on the airplane?