I’ve been amazed at my Pearl Izumi Attack socks. I got a bunch for running, but once I saw ’em I knew they’d be good for this hot spell – so sheer on top, so comfy on the bottom.
I loved the Shimano SPD sandals before the design revision of a couple of years ago. I used up two pairs, and did most of my hot weather riding on them even when I was otherwise dressed up as a roadie. The new design added a mid-foot velcro strap and/or a liner, so they’re far less open. I tried on the original Keen SPD sandals and they were too narrow for me, but the later models are a bit wider though still very narrow.
When I must wear shoes I’m pretty happy with my Bontrager Race MTB shoes. They have a very light mesh top and they’re totally unsuitable for colder weather, but these days they’re just fine.