I teach at a community college,and I'm shocked at how many of my low-income students (most of whom are racking up hefty student loans) spend $4 for a cup of coffee and $8-$10 for lunch each day without thinking twice about it.
Since I advise the student newspaper, I was able to get a full-size refrigerator, microwave, coffee maker, and toaster oven for the space. I encourage students to use it just like I do. I've found that the act of preparing my own lunch in front of them sets a good example, and I've converted many to the idea that you don't have to eat at the cafeteria just because it's there. Seeing me actually do it makes more of an impact than wagging my finger at them and telling them they're wasting money.
Once I show them the economics of paying people to cook for you and brew your coffee, vs. doing it yourself and keeping that money (or not borrowing it), most of them see the light.
Now, if I could just convince more of them to ride the bus to the college--they get a FREE bus pass, and most never even use it--instead of financing a car using student loans, I'll feel better about their future economic situation. Again, seeing me do it makes it less foreign and doable, so maybe I'll pull more of them over to the the frugal way of thinking.