Depends if you're going to eat it on the plane or not. If not, Anepalco's on Main St. in Orange (exit La Veta and turn right, then left on Main and it's on your right). Get the chilaquiles. Big enough for two, just probably won't taste as good cold.
If you are going to take it, then go to Harry's Deli in Sky Park Circle. (Check hours—it's a lunch-only type of place.) They make everything from scratch—including the mustard and mayo. And you can head a little ways down Sky Park to Blackmarket Bakery for sweets. It's just off the end of the runway.
17941 Sky Park Cir, Irvine, CA
17881 Sky Park Cir, Irvine, CA 92862
Off the McFadden exit of the 55:
Tacos El Chilito. Hole in the wall taqueria. I get the torta milanesa. Don't know how the fried, breaded milanesa will hold up as takeout, tho.
Peter's Gourmade Grill: The burgers are good. Odd hours, so call ahead and verify they're there. It's in a gas station.
Taco Pronto: Further off the 55, but the tripas tacos are what I like here, as well as their home made salsa quemada. Other meats are decent, if you're not a fan of intestine, but the tripas are my favorite.
1714 E McFadden Ave, Santa Ana, CA 92705
15852 Pasadena Ave, Tustin, CA 92780
Peter's Gourmade Grill
16851 Mcfadden Ave, Tustin, CA 92780