In the beginning of the story (means end of Memento) Leonard wore Jimmy's cloths and there was a paper in Jimmy's cloths this was how Leonard met Natalie. Why did Leonard do that?
We don't know for sure why Leonard takes Jimmy's clothes and his car after killing him.
All definite facts the movie tells us about his motives, is Leonard's line when he does it:
I'd rather be mistaken for a dead guy than a killer.
There are a couple of reasonable theories:
- He wants to escape the guilt of being a murderer, so he takes over the identity of the victim instead. He is lying to himself to be able to keep going, which is a motive of the movie.
- He simply does it because he likes the expensive car and the clothes more than his own. He takes over Jimmy's life, including his girlfriend Natalie. This might even be a routine thing he does after killing someone. Maybe that's how he got his last car.
- He wants to punish the supposed rapist of his wife even more by not only killing him but also stealing his things.
- It could be simply a plot device to put the events of the movie in place. If he doesn't take his car and clothes, he will not meet Natalie.