So, you're on ASU's campus surrounded by throngs of Cali-Wannabes and fellow heat-strokers. You don't want to wait 3 hours in line at the Memorial Union, or you're trying to avoid undergrads altogether. If you're on the west side of the Tempe campus (close to Mill) then I suggest you think about going to Sack's. Clearly, the best thing about this place is the location. You can walk to Sack's from the MU in less time than it takes to get to your car.
But the food is pretty decent too. Given that they're working with something as everyday as sandwiches, Sack's do some good stuff. They offer traditional American cuisine (club sandwiches etc), tasteful variants (Southwestern and Italian styles), and even some vegetarian/vegan offerings.
Pricewise, it's not as cheap as Subway, but then well worth the extra mile hike in the heat.
PS- not open for dinner