The SLAC cafetera (SLACafé) is located on the 2nd floor of the new Science User Support Building (#53) Cafeteria. It is open for breakfast and lunch on week days. Other alternatives and online options:

• Starbucks kiosk near the Guest House open week days 6:00am-5:00pm. 
• Eric' Gourmet is a Deli at the nearby Sharon Height Shopping Center, which is a 14min walk from SLAC. Many people from SLAC goes regularly for their sandwich and panini. 
• Quadrus Cafe which a 10min walk cross the street. A popular alternative for many from SLAC.
• In case you missed lunch/dinner hours, the Safeway supermarket in Sharon Height Shopping Center has deli,bakery with heated/heatable food and opens 24 hours, and it is 13min walk from SLAC.

Once in a while it may be a good option to take the free Marguerite Shuttle to Stanford campus for the various dining options there combined with a campus stroll. The SLAC line operates between week days ~7am-9pm (see schedule). The various Stanford dining place are described at the Stanford Dining page, and also shown on a special version of the SLAC Line map. Among the large Dining Halls with many stations, only the Lakeside and Arrillaga Family Dining Commons are open for the summer. Arbuckle Pavilion is another good option. Most of these places have a summer closing time of 2:00pm which only leave a rather short time window after SSI morning lectures. 

Disclaimer: While the relatively few places near SLAC are easy to point out, there are 200+ restaurants in Palo Alto and Menlo Park area which are within 15min of drive, and many are good lunch places. The list here is therefore from a rather limited sampling knowledge to just point out a few more commonly known around SLAC, while you should consult more general guides such as Google Maps, or yelp which have more reviews for many places (also check Palo Alto, Portola Valley). If you are really interested in the broad range of restaurants but challenged by transportation, delivery by Waiters On Wheels for a collective order may be another option. Below are some suggestions for nearby places for a simple lunch (plus just a few places a bit further out from choices of many). Click on the full screen mark on top right corner to view larger map. Click on individual places for more info.

Extending topic to dinners, the above disclaimer applies even more strongly as it becomes a rather subjective choice. For  those who really don't want to think about it, there are some specific recommendation lists you are welcome to consider:

• SLAC ATLAS visitor info local dining page
• Cosmic Frontier workshop (Mar/2013) restaurant suggestions 

which maybe not all up to date, as some places such as Round Table Pizza, Hunan Gardens and Zibibbo are now closed. 

Note that US restaurants (and shops) list item price before tax and a 9% sales tax will charged on top of the listing price. In addition, tips to services are not included in the price in most cases and you are expected to "voluntarily" add roughly 18% of the total cost before tax as a tip in case of sit-in dining at restaurant served by a waiter/waitress (their wage largely come from that), which can be cash left on the table or written in to credit card bill.