If you are visiting southern California, I highly recommend devoting a day to visiting the Reagan Presidential Library in Simi Valley. It's about an hour's drive northwest of the downtown L.A. area. Whatever your political persuasion, there is no arguing that Reagan's time in office was a particularly critical time in our nation's history, and museum visitors will draw true inspiration from the amazing exhibits, movies, and audio tour.
We'd eaten a large breakfast before making our way to the museum, since we figured we'd just grab a snack while at the museum. And that's what we ended up doing. There's so much to see at the museum that we didn't want to take too much time out to eat, but if you do want a "sit down" experience, there's "Reagan's Country Cafe" with sandwiches, soups, salads, and snacks. I'm sure there are items that would be safe for gluten free diners, but we didn't go into this restaurant. Instead, we opted to grab various snacks at the Reagan Pub (the bar was donated and transported to the Library straight from a family in Ireland) in the Air Force One Pavilion (yes, they have Air Force One used by 7 presidents on display!). We were delighted to find a basket full of gluten free cookies on display in the Pub, along with yogurt, plenty of drinks, chips, salads, and Santa Barbara gluten free snack bars (both the cookies and snack bars were outstanding!). Clearly, they were thinking of gluten free folks. So no need to take your own snacks if visiting the library, but if you do want to have a more hearty sit-down lunch at Reagan's Country Cafe, I'd call in advance of your visit to inquire about the gluten free options available.