We want you to be comfortable, so smart casual is great, but feel free to dress up as much as you like.
Just be aware that it is an outdoor wedding, so stilettos might not fair well on the grass!
(Trainers are perfectly acceptable.)
If it is hot, you might also want to bring something to swim in. And those of you who do martial arts might want to bring a gi, as there will be a few mats laid out for people to use.