Don't over think this one, it's just a few drinks with your mates. A polo and chinos are a great option, it says stylish without too much effort.
It's all about the smart/casual style. A blazer is a great choice for this occasion - wear with jeans to keep that casual side of the look.
Keep it classic for this one, you still want to look the business but add a fashionable touch with this trendy contrast shirt.
It's time to suit up; it's all about simple, slick and stylish here. You can't go wrong with a cool grey suit and crisp white shirt.