If your current shoes are a bit floppy, you may want to consider some stiffer-soled ones. Some trail /hiking shoes have a good stiff sole which is obviously good for off-the-bike activities.
Shimano leisure shoes are also quite good even without clipless pedals, and I have walked comfortably for miles in them.
Nylon mesh is good for hot summer cycling. Avoid chunky soles and moulded side-bits.
I wear short cotton/coolmax tennis socks. Cycling in knee-high socks is so very 1970s.