Jeans, dress shoes, matching color belt, solid color T-Shirt, Sportcoat or
jacket. But they have to be nicer jeans - nothing with holes in them or anything like that.
Or
The same thing as above, but with a simple 1-color long sleeve button shirt
Or
Dress slacks, button up shirt with the sleeves rolled up. You'll want a jacket with that, but can take it off.
The most important part is going to be the shoes. Get a nice pair of Allen Edmunds (Probably $400-$500) and keep them polished.