Flashes are lovely things to have and indeed I have matching flashes for most of my kilts.

But they are not mandatory and should most certainly not be worn with scrunched down socks. Even with full kilt hose I would never wear a sgian without flashes even if sometimes I wear flashes without a sgian.

The fun bit is going through the drawer trying to find the matching set of flashes for a kilt when I want them!