A 5k food box is an item in Evony TKR (The King's Return). It can be found after killing certain monsters or bosses, with some of them listed below.
The description of 5K Food Box in Evony TKR says:
Use it to gain 5,000 Food.
5K Food Box is known to drop from a number of bosses or monsters upon killing, including Zombie, Redcap, Centaur, Skeleton Dragon, Werewolf, Manticore, Yasha, Peryton, Minotaur, Griffin, Pumpkin Monster, Cranky Snowman, Senior Nian, Medium Nian, Junior Nian, Ifrit, Kamaitachi, Fafnir, Lava Turtle, Warlord, Golem, Witch, Royal Thief, Behemoth, Phoenix, Junior Hydra, Medium Hydra, Senior Hydra, Viking Icebreaker, Viking Berserker, Viking Chief, Senior Bayar Knight, Junior Knight Bayard, Jormungandr, Typhon, Junior Cerberus, Medium Cerberus, Senior Cerberus and Ymir.
Note: This list may be incomplete.
5K Food Box is known to potentially be obtainable from opening Junior Alliance Boss Package. The links for each item are below:
Note: This list may be incomplete.