How can I hide the backpack?

The line StarterGui:SetCoreGuiEnabled(Enum.CoreGuiType.Backpack, false) would do the trick, which disables the default backpack. After that, to disallow players from equipping anything, I think there’s some other topics that described this before:

Also creating a whole custom backpack system is quite a stretch. I think I’ll leave you to attempt this before further assistance.