I have $10 worth of lunch, I eat it, it's gone

I have $10 in cash, I spend it to buy a lunch and eat it, it's gone too. But, that $10 note now becomes the income of the restaurant, they will spend it later, which will cause another $10 income for another guy, and so on...

In the first case, I ate a lunch, did not create any other economy activity

In the second case, I still ate a lunch, but I created a serial of economy activities

Why such a big difference just because the existing of currency? Is there something fundamentally different in the currency than general goods/services?