This is your package = Это твой пакет.
"Пакет" is masculine, therefore the right form of the pronoun is "твой" (also masculine).
This is your idea = Это твоя идея ("идея" is feminine so the pronoun is feminine as well).
Case: Nominative.

These are the remains of your package = Это остатки твоего пакета.
Gender: Masculine;
Case: Genitive (because of the "of" showing possession).