What is a loadout?
Before a match you pick which special items to bring from what you own — they're reserved, and anything unused comes back.
In the Bombermania lobby you'll see a “Your loadout” picker showing only the items you actually own, capped at how many you have. Pick what you want to bring into the match.
When the match starts your picks are reserved from your inventory — held, not spent. Afterwards you only lose the charges you actually fired; anything you didn't use is returned to you. So how you spend your items is a real decision.