Korean vendors have a custom they call "service" (said "service-uh," as most syllables end with a vowel sound in the language) in which they give small gifts to their customers. It's almost like tipping in reverse. Service stations give packs of tissue or bottles of water when you fill up your tank, pharmacists give small bottles of health tonics or vitamin drinks and I usually leave the store where I buy haircare and beauty products with a selection of samples, few of which I understand. Similarly, if you shop at the same market regularly, the employee weighing your produce is likely to throw an extra handful of salad greens or piece of fruit into your bag after it's been weighed and priced, as service-uh.
When I lived on Jeju Island and did my vegetable shopping at the traditional markets, I learned to only buy half the amount I needed, so generous were the grandmothers I returned to buy from every five days. Even the coffee shop I frequent in my office building, in addition to having a frequent drinker plan, packages up a piece of cake for me when the whim strikes. Not having the Korean for, "I don't eat cake, unless it's sinfully decadent chocolate cake," I thank them profusely and give it to a cubicle-mate.
Many Korean-owned restaurants are the same and I, being a light eater, often find myself with more food than I ordered or could possibly eat. There's a reasonable Mexican restaurant close by that I go to about once a week and my serving sizes have been steadily increasing.
Today the staff went one better. Not only was my tostada larger than I could manage and packed with extra beef and avocado, but it came with a shot of tequila. For lunch!