It is personal policy that whenever I am on the West Coast I have to search for nearby In-n-out burger joints. If you have never been, there is a reason why they are always packed. With a focus on quality, this is the best fast food chain in the United States. You have to know going in that there will always be a line and parking lot craziness. With that said it is well worth it. If you're up for it, get the fries "Animal Style," which adds grilled diced onions, cheese and a "special sauce" resembling thousand island of sorts. You might as well get that Doubledouble...
This particular location is just off the Strip in Vegas, really close to the New York casino. It is a bit of a pain to get there by foot but a lot of folks do it. Short cab ride also an option.