What's "this is it" mean? When's this expression used?

Native speaker’s answer
Rebecca
Here, "it" refers to the food. The speaker is basically saying "this is [the food] in the delivery car," and he even shakes the box strongly to show how food often gets moved around while being delivered. However, the way he says this sentence sounds a bit awkward. It would have sounded more natural if he used a noun (like "the food," "the box," etc.) instead of "it" here. Typically, "this is it" is used to announce something, like when somebody has arrived somewhere or seen something they have been waiting for. Ex: This is it! What we've all been waiting for. Ex: This is it. Are you guys ready?