Da, imam nešto za prijaviti means “Yes, I have something to declare”. The second half is identical to the sentence before; only the beginning is new.
At customs your dad is standing there eating a date: since both start with a D, the date stands for da. You and your mum are sitting in the fog at the back with a box of tomatoes that you are salting – mum, box, tomatoes and salting give you imam nešto za. Then comes the pinch from the jacket and the beastly good tea from the last video for prijaviti.
Write the story down and say it out loud several times, but give yourself two or three days. Grass does not grow faster if you tug at it: at some point you will not need the date and the fog any more, and the sentence simply comes – like a song you can sing.