Some questions I have been asked, along with people I know who were targeted and harassed when flying post 9/11
Again, doesn’t mean it’s going to happen to you, but something to consider since you might not be allowed through without cooperating:
Where are you going
Are you traveling with anyone
Who are you going to see at destination
What are you going to do at destination
How much cash did you bring
How much money do you plan on spending
Did you bring gifts for anyone
Did anyone send gifts back with you
Where are you staying (sometimes exact address)
Who are you staying with
How did you book your accommodations (sometimes they request to see receipts)
How will you be traveling while there (car, public transit, etc)
Have you been there before
While some of these are not uncommon for international travel, many of these have been asked while traveling domestically too. On one of my most recent flights, I was asked a lot of these questions very informally. A dude with DHS was pretending to shoot the shit and it almost felt like flirting (but was very transparently questioning me)