I wear my UKs more or less just like I wear jeans. Sometimes I wear a button down, casual shirt, sometimes a t-shirt. Some times tucked in, sometimes not. If it's chilly I'll wear a sweater, sweat shirt, henley or maybe a piece of fleece. Often I couple a UK with a jean jacket. If it's hot I'm in flip flops (I'm not partial to sandals), but usually I'm sporting a well worn pair of 6" black leather boots (that I don't bother polishing) and scrunched down kilt hose. In my view, there are no "have tos" with UKs. Wear it how you want and don't let the stuffy kilt police tell you otherwise.