While in Salt Lake City, get to the area around 800 South and State; in that area there are at least 8 or 9 street vendor taco wagons and they are all good, some of them very good. Also, the Fullmer gym is in West Jordan, but it has recently moved.
If you hit the Grand Canyon, at this time of year it is much less crowded if you go to the North Rim. Take highway (??) 9 east out of St George Utah. But while you're in that vicinity, don't overlook Zion, Bryce, and Capitol Reef National Parks. That whole 'canyon country' area is truly spectacular. Monument Valley is right there as well.
The Canyon De Chelly national monument is a bit of a drive, close to the New Mexico border, but check it out on-line; really something to see, and they have a good gym in Chinle.
From Mesquite, Death Valley isn't too far and the "Extraterrestrial Highway" will pretty much take you there. A bit north is the Great Basin National Park, which I haven't seen, but I've read and heard that it is worth seeing. Glaciers in the desert!
There is a lot more going on in Salt Lake than you might think; a pretty thriving music scene and so on. Get out and explore a bit.
Have a good time, my friend.