Generally t-shirt and jeans. I wish I could get away with wearing shorts more, but I think I look a bit too ridiculous in em, even though I prefer them. If I get really cold (shop is 40 degrees or lower) I'll toss on a sweatshirt in the winter.
My t-shirts and sweatshirts generally have my logo on the front with name, and an advertising blurb on the back, and I rarely wear anything else, free advertisement!