The lack of responding to an argument or confrontation in a mature manner in a relationship means the relationship will never stabilize. Arguments are part of the relationship and there are occasions to disagree because we are all different with different opinions. What matters is not whether we disagree but how we can approach a subject we don't agree upon.
This means there would be no point in getting back together if he can't keep up with an argument or relationship in a mature manner, instead preferring to break up with you.
You should act as if you barely know each other. This doesn't mean you ignore him or somehow talk rudely or treat him like he doesn't care.
You should treat him like someone you started knowing the previous week, signifying you don't know much about the person.
You might inform him you want to come for your packages, or if you prefer, go unnoticed. In this last instance, you know he'll be present at the time you're going to his place.
After knocking the door or pressing the bell and him opening the door, with a smile (though you're hurting, try to do so naturally) greet him, "Hi."
To avoid any form of uneasiness, ask how he's doing. After he has responded, let him know you're doing well.
Use polite language when asking for your package.
You: How are you doing?
Him: I'm doing good. (He might stammer). How about you?
You: I'm also doing good (or any answer close to that showing that you're working on moving on).
You: Uhmm...sorry to disturb you but is it possible to hand over to me the packages that belong to me?" (Or, "I have come to collect my packages. Please, is it possible to hand them over to me?"). You can use your own words whereby you ask politely for your things.
Don't show a face that is registered with rage or disappointment or any other that shows you've come for your things and you don't care about him.
Don't linger for any conversation or to talk about the failed relationship. Decline politely. Let him know, if he asks, you need time to be on your own. You will respond to him once you've come through the breakup.
When he has handed over to you the package, say, smiling, "Thanks. I have to go now."
Being polite acts as an insulator or shields you from anger and hatred that can erupt from seeing him. Also, from not feeling pain at its highest level from seeing him.
Don't accept to enter in. Anything might happen inside there. Ask him to bring them on the outside.