One outing we enjoy when we go in October or November is to go hiking at Cheakamus Lake. It is close to Whistler and gives you an up-close-and-personal look at one of our beautiful B.C. forests. If you can, bring a picnic lunch to enjoy at the lake.
I don't know if you're planning to rent a car, but if you drive a little bit north on the Squamish highway, you'll find Alta Lake. It is a beautiful lake where you can rent canoes (not sure if you still can in Oct., but you can ask at your hotel).
You can go ice-skating, check out the cuisine at one of their fine restaurants, go shopping (some sales, I think, at that time of year before their winter stock comes in), soak at your hotel's hot tub, take a swim, visit the beautiful Chateau Whistler Resort, etc.
Have fun!!!