This article is a Ninja Wannabe's paradise. Read on if you want to dress like a ninja.
Wear a T-Shirt that will blend into your surroundings such as white or grey for winter to blend with the snow and make it into a ninja mask. (for more info copy and paste this to the wikiHow search bar: "How to Dress Like a Ninja Using Only a T-Shirt")
Get another shirt (long sleeved) of matching color and put it on.
Then get sweat pants of matching color and put them on. Sweat pants work better because it lets you move around more, if you don't have sweat pants you could use jeans, but keep in mind that it will restrict your movement more than using sweat pants.
Then get a pair of socks that will match the color of your outfit and put them on. You do not want to be dressed in black and put on a pair of pink socks, do you?
Then go buy some shoes of matching color. You can use any pair of shoes that you can walk reasonably quietly in, don't use anything that will give you away! If you want to get really into it, you could get yourself some barefoot running shoes, but beware of dangers such as glass!
Get yourself some ninja weapons and have fun! You could use paper ninja stars or make yourself a ninja sword.
If you have extra fabric that matches your outfit, you could cover your shoes with it.