The first rule of costume recreation is that you don't talk about...
A pair of red sunnies come next. The real deal will set you back roughly $1000, but you can find knockoffs on ebay at a fraction of the cost.
We sourced the old man golf pants at our local thrift store (Tyler sports a pair in his very first appearance in the film during the "ass or crotch" sequence). Ditto for the faux fur jacket-o.
Add a cigarette (fake or otherwise), prop pistol, and smeared blood and you're ready to rock. The alter ego? That's on you. In the words of the man himself, "Just. Let. Go."