Don't spend money on things you don't need.
Only buy food that you need and cut down expensive habits such as Soda.
Cook at home. I can buy 20 hamburgers from the grocery store for $5. That only buys me 4 hamburgers at McDonalds, the cheapest of cheap fast food joints. Plus pasta and canned veggies/fruit can be purchased for less than 50 cents each.
Take advantage of potatoes. I can buy 10 pounds of potatoes for $2. There is no other food that I can get that volume for the price. A baked potato and a half a chicken breast makes a pretty good meal, add some salsa to it and you have a cheap variation.
There are lots of free or extremely cheap things to do for entertainment. Buy a notebook, (I just bought some for 10 cents) and write your life story. You can keep busy for months on the cost of paper and pen (total less than a dollar).
Go to the discount rack at Barnes and Noble. You can get books here for $3 that will keep you entertained for weeks. A bonus is that a book lasts longer than a movie and keeps your mind more involved.
Teach yourself to draw. For the costs of pen and paper, plus the cheap book from B&N you can stay busy for months. This could maybe even turn into a money making venture if you find you have a talent that you never knew about.
Go for a daily walk. Walking cost nothing and doesn't even require any kind of investment in clothes.
Exercise. A rubber band exercise set can be purchased for $10-$15. This can offer resistance training for most exercises. The last one that I purchased came with a chart of over 50 different exercises to do. Do this for 45 minutes a day.