What are the key items to buy from the Grocery store?

I'm 21 i don't live at home and i have to learn a lot of things on my own. That said i know that there are a couple things to keep on hand: eggs, milk, bread, condiments, cereal. But beyond that making meals at home appears to be very expensive for only one person. Here's Why: Chicken $5 rice $4 vegetables expensive so when you do the math out one meal is like 6 dollars for that i could go some where and buy a meal. i'm hoping to spend less than $300 a month on food less than 10 dollars a day. without being too unhealthy is this possible?