Jeans, t-shirts, timberlands etc etc etc. If you go too fashionably you'll stick out like a sore thumb. Take a second jacket to your ski jacket and don't even think about taking something smart for one night.... you'll never need it!!
moonboots are not realy needed if you are staying in the centre of borovets, but you do need footwear with a good grip.
Most of the bars are all within 3 mins walk, I just take my trainers and walk carefully.
We found the snow in the town very compacted and at times dangerously icy - so as Chiro says wear something with a good grip sole and if this is your moonboots then those will be just fine. We wore ours!!