1) Add a counter top. Even if you simply bring your prepared meats and veggies outside, have a landing surface for you plates, cooking utensils and other items needed during cooking.
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2) Provide a light source. many grills have built-in LED but that isn't always sufficient. If you don't have an overhead source, try goose-neck fixtures, outdoor lamps, and strip lights around the perimeter of your cooking surface.
3) Have storage. Hiding a propane tank, storing cooking utensils and keeping everything you use outdoors, out there will make using the space easy and efficient.
4) Install a sink and necessary appliances. Not everyone needs an outdoor wine cooler, but a small beverage fridge for cool drinks, marinades and other items is nice. A sink for rinsing is almost always a must-have since clients that don't have one installed initially always add it later. For very large outdoor kitchens, a dishwasher is a convenience.
5) Consider a roof. Even a trellis can be nice to provide shelter from too much sun, a place to install lighting, and a protective cover from rain.
6) Add a hearth. A source of heat and warmth is wonderful for cooler nights. You can use outdoor kitchens in colder climates for a longer season.