Stay in a treehouse at the Salt Spring Island HI - book in advance.
Explore the tiny islands around Salt Spring by taking a boat or canoe out for a day.
Wander round the Saturday market in Ganges and come home with delicious organic farm produce or a bag full of wood carvings and bright fabrics that you don't really need.
Quick Tips:
Best Way To Get Around:
Hitch a lift - all the backpackers do it and most locals will be happy to help as long as you don't mind sharing with a boisterous dog or three.
Bike - hire them from the hostel or in Ganges.
Walk - but the island is bigger than you expect!