Boost will be selling another kind of item or can be obtained within an iron lockbox. The actual item is more expensive when purchased from Boost directly if you're too lazy to get an iron lockbox.
The items
-Large Belt : Increases the limit of pickups per slot by 1.
(The normal is up to 3 pickups per slot)
-Long Belt : Increases the number of slots in your belt by 1.
(The normal is 4 slots in your belt)

Please tell me if you have more ideas.