In Southern topolects — Cantonese, Hokkien, Hakka — the verb 'to eat' is 食 (sik6/chia̍h) rather than 吃. You'll see 食饭 on HK/Taiwan/Guangdong menus and signs; Mandarin 普通话 drops 食 in favor of 吃.
register
Classical Chinese also used 食 for 'eat' (食不语, 寝不言 — Confucius). So 食饭 is both a Southern colloquialism AND the historically older form. Xinhua-ci glosses 食饭 simply as 'a meal'.
