First of all, Welcome to the Roadfood website. I moved your thread to the forum that we hope will draw the most responses for you.
Good luck finding a ‘cool route’ between Vegas and Portland at this time of year!! I have done the drive many times in all seasons, and this is probably the least comfortable. That Said, here are a couple of thoughts about routes to use.
1. The easern slope of the Sierras is higher and therefore probably a bit cooler than the desert valleys of Nevada. Use US 95 to the US 6 junc. at Coaldale NV. Take US 6 into California the 120 to its crossing of US 395. It may add a few miles, but it is quite scenic and much cooler. A couple of decent cafes in TONOPAH (Home of the Muckers) Nevada !
2. Then go north on US 395. It stays in the mountains all the way into Oregon, except for the urban area around Carson City and Reno. Use US 20 west from the Burns,OR area to Corvallis and you are close to home .
3. Our last ride down US 93 from Idaho to vegas in 2004 was outstanding…Empty roads for miles and miles, but little to attract the eye or the tummy anywhere. Plus it was February so it was in the 20’s not the 100’s as it is today. Nice ride, but not a summer fun time.
4. US 95 from Reno to Idaho is also very empty, but adds quite a few miles to your trip.
Food, My one big suggestion is to be sure to visit LOUIS BASQUE CORNER in Reno. Doing a search for Basque food on this site will give more possibilities, but Louis’s in Reno is an institution and well worth a visit. This is NOT light-snack food. Basques like their meals to be ‘filling’ and these are. But for the end of a day’s ride this is a great dinner to enjoy.
Hope this helps.