I usually wear them with t-shirts, but I just happen to be OLD, and so I tuck in my t-shirts. If I'm backpacking or doing something strenuous, then the shirt may have cut-off sleeves.

Boots. I just think that substantial shoes/boots look better with any sort of kilt. I, personally, for me just don't like the sandals and kilt look. That's just me, eh? Y'all can do whatever you like.

Biggish belt. My two "utility" kilts are kilts I've made for myself and they don't have pockets, so instead of a sporran I use a black fanny pack with the load-carrying part up front.