“Ta med sekken inn, og sett den under setet ditt.” meaning “Put your bag inn and put it under your seat.”
Why did she not say “Ta med sekken dine inn og sett den unter setet ditt.” Why did she use the possessive adjective “dine” or “ditte” meaning “your” only once, when in English, it implies that it should have been used twice.
If Norwegian is anything like Swedish or German in this respect, then it might be the case that they don’t say “your seat” because it is kind of obvious that it is your seat because you are sitting on it.
In German, you can say things like “I put the hat on the head”, because, if you think about it, you very rarely put hats on other people’s heads 
And in Swedish, they don’t even bother with a definite article, you’d have something like, “I put the hat on head”.
The hat on head example is completely made up because I can’t think of an actual real example, but I hope you follow what I mean anyway, @daisy2chain
Thank you.