The Rainbow Drive-In is fast food restaurant. It was Hurley's and Sayid's first stop after Hurley's escape from the Santa Rosa Mental Health Institute. They were helped by a counter girl. ("Because You Left")
Rainbow Drive-In is one of Hawaii's premier "drive-in" restaurants and has been since 1961. The place serves local-style favorites for rock bottom prices. There are some restaurants from the chain outside of Hawaii, but apparently not in Los Angeles.
Actual location may be 3308 Kanaina Ave in Honolulu. (Google Maps Street View)