What's the word that describes this ability/quality?

What is the word that describes someone who displays the ability to think of alternative ways of dealing with a situation, especially a situation that calls for it and then acts upon it? In my native language, it is a relatively common word. As I thought of it, the idiom think on your feet, and the word nimble sprang to mind. It is the closest expressions I could think of, although it is similar, it does not contain the exact meaning of that word.

Basically it's an adjective that describes someone who's able to quickly think of alternatives in a situation, especially in a situation that calls for it. He is able to accommodate to new situations as opposed to someone who, if faced with a similar situation, will become stuck, not knowing what to do and unable to think of any alternatives.

For example, If someone who's shopping for ingredients for the desired dinner he's going to prepare for his party guests discovered that one of the ingredients for a dish he's going to prepare is not sold in any of his local grocery stores, he buys another similar ingredient as a substitute. He is (that word), because he has the ability to think of alternative ways in dealing with the situation where as someone who is not (that word) is rather dull and when faced with such situations, will propably decides not to prepare that dish and may also get frustrated/upset over the matter.

Solution 1:

I would think of flexible or adaptable as well.

Solution 2:

Consider imaginative (“tending to be fanciful or inventive”), resourceful (“Capable or clever; able to put available resources to efficient or ingenious use; using materials at hand wisely or efficiently” (emphasis added)), plucky (“Having or showing pluck, courage or spirit in trying circumstances”), and creative (“Tending to create things, or having the ability to create; Original, expressive and imaginative”).

Solution 3:

In addition to jwpat7's one-word solutions, there's the phrase "able to think outside the box", which combines imaginative and creative. Distant relatives in this context are intelligent and quick witted.