I'd say clinging is when we pick up and constantly play with the idea of something, even when we are doing something unrelated. For instance cleaning your kitchen, but spending the whole time obsessing over a new item of clothing we fancy buying. Do I want the black shirt or the blue one...? Maybe the ladies will like me in my new shirt.... Clinging is something that takes you out of what you are doing here and now, and places you in a fantasy world. I'd say this is the simplest way to tell if we are clinging.
Noticing that you are hungry and subsequently, mindfully preparing a small healthy meal, then eating it mindfully, isn't necessarily clinging because you're not obsessing over it, you're just listening to your body and acting accordingly. That is not to say any time we eat when hungry is free of clinging. We might gorge ourselves on unhealthy junk food whilst fantasising about what we can do afterwards. However it is possible to fulfil a need without clinging.
A discussion on all aspects of Theravāda Buddhism
"If only it were all so simple! If only there were evil people somewhere insidiously committing evil deeds, and it were necessary only to separate them from the rest of us and destroy them. But the line dividing good and evil cuts through the heart of every human being. And who is willing to destroy a piece of his own heart?"