Clue: 21st book of O.T.: timeless casket displayed food containing fruit (6,5)
Answer: ECCLES CAKES
Explanation: Definition: food containing fruit
A charade of ECCLES (a standard abbreviation for Ecclesiastes, which in the Protestant Bible is the '21st book of O.T.') plus CAKES, an anagram ('displayed') of 'caske[t]' minus the T ('timeless').