Polo style or short sleeved broadcloth casuals in solid colors are great for summer if you want more than a t-shirt. And some lighter weight hose like W.Brewin sells,
http://stores.channeladvisor.com/wbsocks/Kilt%20Hose/
I personally like to match the hose and shirt, so when getting a new kilt or hose combo, I'll take the socks to the mall and match them up..