Couldn't help myself for a moment...
I'd skip the flight to LAS.
I'd say brings lots of map, if you're getting a rental car and allow 1 1/2 times non-rush hour traffic time in rush hour. Bring pen and paper also to figure out sidestreets in case the freeway is a mess because of an accident or something.
If you are going from airport to airport, you might want to consider the following:
http://www.supershuttle.com
http://www.primetimeshuttle.com