"I have olives."
Olivae = THEY, the olives: a nomin. plur. 1st declension form, used as a subject: The olives please me (I like the olives): Olivae mihi placent. The olives are on the table: Olivae sunt in mensa.
Olivas = THEM, the olives, an object form, accus. plur. Livia buys olives in the market: Livia olivas in foro emit.
Olivas is in the plural, panem is in the singular. Also, "oliva" is 1st declension feminine and "panis" is 3rd declension masculine. Who has it is irrelevant.