This is a very easy costume to put together as you probably have many of the components in your wardrobe before we even start.
The pants that Katniss wears in the movies were based on a Levi Strauss 1870s pattern and are a brown striped jean, but you could wear a pair of plain brown or even olive colored jeans and still be unmistakably Katniss Everdeen.
The next important part of the costume is the old leather jacket that Katniss wears to go hunting with. With this jacket costume designer Judianna Makovsky actually deviated from the book - in the book Katniss' jacket was oversized and a hand-me-down of her fathers, in the movie it was a fitted leather jacket. Makovsky says that this was so that Katniss could move her arms easily in order to actually use a bow and arrow.
You can search through thrift shops or wardrobes of older male members of your family for an oversized leather (or leather look) jacket or you could just buy a fitted jacket that you can use in your everyday life as well as when you're in costume.
Underneath her jacket Katniss is wearing a crew necked thermal shirt with buttons - this was also handed down from her father and you could look in a thrift shop for one, although I like the henley style shirts as you can also incorporate them into your wardrobe once you've worn the costume.
Footwear is another important aspect of Katniss' wardrobe - this girl is practical, no pretty stilettos just plain boots which allow her to easily traverse the land in order to hunt her prey!
Of course you need to accessorize this outfit a little so that no one is in any doubt about who you're trying to be and luckily you can do that by buying a replica bow from the movie which I've also found for you opposite.
Next you have to give yourself a side braid or if you want to be even more authentic try a Dutch braid (instructions are in the Katniss Everdeen's Hunger Games Costumes article below).
There are more costume ideas for Katniss from her 'uniform' at the training center to what she actually wore during the actual Hunger Games and let's not forget Katniss in a dress! You can check those costumes all out at the article below.