For casual wear in summer you can't beat a Hawaiian shirt. Whoever invented them must have been a concealed carrier. They look natural untucked and you can hide a howitzer under there. I purposely buy them one size larger because they look natural baggy too, and I can conceal better that way.
I also buy tall size t shirts and polo shirts for wearing untucked. I have to buy those online because everything decent I find in the big and tall shops around here is for big, not tall, and I'm not fat, at least not yet. Here are a few of my sources:
Printed Apparel: Big, Tall, and Plus Size Clothing
Patriotic Shirts & American Flag Shirts | TheFlagShirt.com
Shoes, Clothing | Zappos.com Free Shipping
Discount Big and Tall Clothing - Big and Tall World
I use four Crossbreed Supertuck holsters with four different guns, depending mostly on the weather and the lightness of the clothing. The Supertuck allows me to tuck the polo shirts in if I want but I prefer not to do that in warm weather because despite what the advertisements say, I think the bulge of a gun on my hip is at least somewhat noticeable.
I also have a SmartCarry holster for my Ruger SP101. Concealment with that is simply outstanding and I can wear whatever I want, but access is difficult and slow.
The Constitution shall never be construed … to prevent the people of the United States who are peaceable citizens from keeping their own arms.
--- Samuel Adams