I just checked and McDonald's pays $15 an hour, no? That's more than enough to not starve.
Also you’re neglecting the cost of transportation (almost certainly a car, with gas and insurance), rent, and medical expenses.
Assuming you work full time, you are making $3360 a month, less taxes.
That means that even if you get the bottom 25% of rents, over half your take home pay goes to rent. Then we need health care, food, taxes, transportation, clothing, etc.
Not a lot of savings easily available there.