The pub's storeroom is at the right of the kitchen door, to the right of the vocabulary game.
Hint 2
The general rule is to take everything you can, whether you know why or not. In this case, that's a canister of gasoline and a disk with a flower on it. Just hold onto them; you'll know when to use them.
Hint 3
And while you're in here, you'll overhear an argument between Gunnar and Elisabet. What an odd man he is!