Learn Spanish (Latin America): Yo veía el trigo empacado.

empacado is the past participle of the regular verb empacar (to pack). To form it, you simply drop the -ar ending from the verb and add -ado. In this sentence, it functions as an adjective meaning "packed".

Would empacado change if the noun were feminine or plural?

Yes! When a past participle is used as an adjective, it has to match the noun it describes in both gender and number. Because el trigo (the wheat) is masculine and singular, it stays empacado. If the noun were feminine, like la ropa (the clothes), it would become empacada.

Why does the sentence use veía instead of the past tense vi?

veía is in the imperfect tense, which is used to talk about habits, routines, or ongoing actions in the past (which is why it translates to "used to see"). If you used the preterite tense vi, it would mean you saw the wheat once at a specific, completed moment in time.

Is veía a regular verb in the imperfect tense?