If you're required to do something with a certain number of things and there aren't that many things available, use as many as there are. For example, if you're told to choose 2 characters at a location occupied by only 1 character, choose only that character. If you're told to draw 4 cards from a deck that has only 3 cards, draw the 3 cards. (Regardless. if you need to do anything with any number of cards from the hourglass, other than shuffle it, and you don't have enough cards, you lose the scenario; if that happens with your deck, your character dies.)
Note that this only applies when you are required to do something. If you have the opportunity to do something that requires a limited resource, and you don't have enough of that resource. you cannot do that thing. For example, if the requirement to close your location is "recharge 2 spells" and you have only 1 spell, you cannot close that location.
When a power or effect refers to 'any number' of something, that number must be at least 1.