As has been pointed out, the Grand Canyon isn't really very near Vegas at all, and would only be worth the round trip if you went by air. Its best seen at sunrise and sunset, and these are not easy to see in a day trip.
I can echo the Hoover Dam ..... Well worth a visit.
Death Valley again is an awful long way away, and is so spectacular, that it would be shame to try to see it in a day trip.
Be wary though of high summer....Death Valley will be punishingly hot.....so hot in fact that some places will be shut.
The Valley of Fire is amazing, and only about 50 miles from Vegas. This would be an ideal place to visit by rental car, taking n the Dam as well. A long day be entirely doable. If you visit the Dam first, and then the Valley, you will be returning to Vegas in late afternoon/early evening, and the view of the city as you approach is magical !
https://www.google.co.uk/search?q=valley+of+fire&rls=com.microsoft:en-GB:%7Breferrer:source%3F%7D&rlz=1I7ADFA_en&biw=1024&bih=726&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiH4byQxe3KAhXFWxQKHfd9BTwQ_AUIBygB
How I envy you if you are visiting soon !.....I haven't been out West for nearly 20 years, and would dearly love to go back one day.