Spawning Items in the Back-Backpack

Hello,

I’ve been trying to look for a way to make players spawn in with items, but not in the first 10 slots of the item slots. For example, if you were to not want a gear, you’d press the `/~ button to open the “backpack” and drag it in there. I want to make it so items spawn there. I guess I could make it so it’s toggleable items, but that’s kind of annoying and I’d like to avoid that if possible.

I’ve tried looking for other dev forums but they are all concerned about a literal backpack instead of the StarterPack gui.

Thanks