I'd take knitted dresses/boots/tights/presentable shoes for semi-casz evenings, then skinnies with nice jumpers/scarves/blazer for day - but prepare to feel out of place, unless things have changed in the several years since I've been.
I asked just the same thing on here a couple of months ago and had lots of helpful advice.
We took food with us so it wasn't too expensive and had a great time. We got there early (about 12 I think), collected our bikes and had a look around and some lunch then went to the lodge and picked the car up later. Take a rucksack!
We spent a weekend there last year and had such are great time, we are going back for xmas For sports type activities I am taking: Swimming costume, flip flops, running tights, running top, trainers, sports t-shirt, fleece top, gilet. For day to day: jeggings, skinny jeans, cord skirt, jumpers, heat tec tops, scarves, parka coat, boots, For evening: jersey dress and pair low heels
Last time we went and got dressed for dinner - husband observed we looked like we were at a wedding compared to everyone else! It is very casual.