If you don't already know, one of the best ways to earn EXP in Yakuza 6 is by keeping Kiryu properly fed. However, what you might not know is that most restaurants found in both Kamurucho and Onimichi have Secret Menu combinations, the same that will see you obtain Bonus EXP for combining said items of Food. By eating these menu combinations at said establishments when Kiryu is hungry, you will earn loads of EXP in no time at all! But also be warned: you won't receive any Bonus EXP if Kiryu's Hunger Gauge is already full, even if you Eat the proper food combination.
Onimichi Secret Menu Combinations (Restaurants & Combos)
Jomangoku Chinese Soba: Large Onimichi Ramen + Large Chashu Onimichi Ramen
Le Pente: Red Wine + White Wine
Le Pente: Oven-Baked Chicken Thigh + Specialty Green Salad + Specialty Strawberry Shortcake
New Gaudi: Edamame + Pickles
Oyster Shack: Fisherman Soup + Octopus Sashimi + Squid Sashimi
Yonetoku: Meat Nabe + Stew + Crunchy Shochu Highball