I should also add, the inventory slots are all time-based (…

I should also add, the inventory slots are all time-based (except the super, Holy Bolts - that one remains until used and it is a one-time-use super). All the other inventory items expire in about 3 minutes. If you see the numbers next to the inventory items, that means you have more than one. When the 3ish minutes is up, that number will go down one. If the number hits 0, then the boost deactivates until you find the item again or trade monster credits (what defeated monsters drop in the game) for the boost in the trade window.