Is it a conference? Assuming that you're female and you tend to wear typical 'female' clothes ie dresses, skirts and tops, sometimes trousers, but not suits like a man would, I'd say for 'business casual' a day dress and shoes that you're comfortable standing and walking in, layers (fine knit cardigan or jacket, but not a particularly structured one) in case the air conditioning is fierce, or a top and skirt or trousers, again possibly with a cardigan or jumper. No denim, hems at least knee length, remember that a skirt or dress might ride up quite a bit when sitting down.
For the outdoor sessions, same as above, consider the weather and that if you have to walk on grass or gravel you don't want pointy heels.
For semi formal, a dress or trousers and nice top if that's more you and nice shoes but not a long evening dress type, dress as if you were going to a restaurant for a nice dinner on a special occasion, again no denim.
My top tip for conference attendance, always go to the toilet before the speeches start. and don't get too drunk