I would second the thrift store idea, what do you have in your closet already you may have almost everything you need, how are you set for kilt hose and flashes? A nice dress shirt and a tie will dress you up right away, but remember that an ordinary tie is too long to wear with a kilt, perhaps you could borrow a clan tartan tie from someone in you clan society, or go out and buy one if you need to. Also I would look at the following threads for ideas:

Dressy:
http://www.xmarksthescot.com/forum/s...ad.php?t=22432

Casual:
http://www.xmarksthescot.com/forum/s...ad.php?t=22431

As you will be in the clan tent all day you might want to bring something a little more casual to change into latter, so you dont suffer in the heat all day.