I think something like flip flops are a good idea. Walking barefooted is fine, until you've got to walk through a muddy section, or in a field which has been grazed until recently, or need to use a less than salubrious toilet & shower block. You can use your cycling shoes, but as others have said, you can end up getting them wetter from dew than a days worth of drizzle would do. It's also a mite annoying having to do and undo the laces just to pop quickly to the loo, or to get in the shower quickly. Flip flops at least pack fairly flat, unlike many other shoes.