I'm more likely to do fast food when I'm on my own, so I can't make any recommendations on
restaurants unfortunately. Just across I-5 from Harris Ranch are a pile of fast-food joints, there's a McDonalds, Burger King, Taco Bell, Carl's Jr., I thought I saw a Subway in one of the gas stations. There is also a Denny's there, it looked like there used to be some other diner/buffet-type place but it was empty. As Thirsty says there are two restaurants in Harris Ranch, I've only done the steakhouse, not sure how much the menu at the other (more like a bar & grill) differs.
TCC's 3-day October Skies last year I stayed at the Motel 6 across from Harris Ranch, had one nice dinner at the ranch steakhouse and did fast food the rest of the time. Previously I've stayed at a Travelodge (now also a Motel 6) in the SW corner of Fresno (I-99 at the Belmont Ave exit, all of the closest hotels/motels are about a 30 min drive away, just in different directions), lots of fast food places around it also (one exit north, Olive Ave), but there should be more local restaurants there as well since it's not just a truck-stop.
The closest gas station (corner of Kamm & Lassen, very close) has a convenience store with a burrito (I think) stand inside it, haven't eaten anything there though so I can't comment on the food, and it might be more of a lunch and maybe breakfast option, not sure how late the stand is open. There's another market on the way from the site to Harris Ranch I've heard good things about (I think it's a deli, though I don't think it's open late, seemed like it was closed every night when I drove by).
Edit: San Joaquin, just a few minutes up Colorado Ave, also seems to have several restaurants (Mexican & Pizza at least, well rated per Google Maps). Have only ever driven through this town, never stopped there.