Minimum:
Kilt
Belt
sporran or bumbag
short socks
shoes/boots
T shirt

This my minimum casual for going out. Around the house I throw on my Bear or USA velcro casual.

I like a belt to hang a cell phone on and I think a kilt always looks better with it.
A bumbag in needed to keep my essentials, money, reading glasses, Palm Pilot.

Socks and boots because i am not so casual as to wear sandals. I might go barefooted on the beach, that's all.
Shirt, for obvious reasons, I like a shirt with a celtic theme. (like a Guinness shirt)