Waistcoat only?

[unixken]

I should think you'd be just fine, with waistcoat, sans jacket.

Two oft-held principles you'll see on this site are:

A) Think of the kilt as simply a replacement for slacks - if you'd wear a waistcoat/vest only, when wearing slacks, then it would be equally ok to wear with a kilt.

B) Weather and climate will certainly influence an outfit. In warmer climates, one can not be expected to wear what one might wear in the often cooler, damper regions of the world. Better to be seen minus the jacket, than to be seen sweating like a dog.