The wingtips, especially with those socks. It'll help pull the outfit together. Of course, you'll want to go with a a different shirt, like a polo or a button-up. Oooh, I'm all tingly so I'd better slow down.

I recognize your sporran. I have one too. Nifty Notions, right? It's a good day sporran for really casual outfits. The small size makes it easier to get stuff out, especially since I only carry my phone & wallet.

You could wear black boots with that t shirt, but go with grey socks, I say. I have some from utilikilt (3/4 leg) that I roll down on my black combat boots.