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Both of these are correct:
1.a. This item is not on the list. <more common, commoner>
1.b. This item is not in the list.
Both of these are acceptable, but 2b follows traditional grammar rules:
2.a. Everyone has their own dream.
2.b. Everyone has his/her own dream.
Try, what would you do? 3a is correct:
3.a. If you were me, what would you do?
3.b. If you are me, what would you do? <Try, Let's say, you are me...>
Both are incorrect:
4.a. hope/wish your dream came true.
5.a. hope/wish your dream come true. <Try, I hope your dream comes true.>
All the best.