In Vegas itself I would start the day with a lunch in the revolving Stratosphere restaurant (very reasonably priced). That way you could get a layout of the surroundings.
After that I would park the car somewhat near the center of the strip (maybe near Bellagio's) and walk both north and south. 1st take in the fountains at Bellagio then go north and tour through the Caesars palace shops - then see the free outside shows at Treasure Island and the Mirage - cross the street and visit the inside of the Venetian hotel and shops - then go south on that side of the street down to MGM and see the inside show of lions etc. - then continue down towards NYNY and take some great fake photos - then head down towards the Luxor (just for the unusual shape of it) and Mandalay Bay to see the marine exhibit.
Of course you could take the car to these place as that tour is at least a four mile course.
I tried to list the best 'free' stuff. Of course if you have time they have great paid shows and I could recommend some but that would take way too much time.
For more free stuff visit:
http://www.vegas.com/attractions/freeattractions.html
And of course as you are leaving LV you could visit the Hoover Dam and then on to the grand canyon. OR you could take a helicopter ride right from downtown LV to see the dam and the canyon.
An 8 hour trip could never do LV justice! My wife and I stayed for 4 days and didn't gamble once!