One of the most dangerous situations for the canyoner is to take a walk near a mental hospital. Infact, what could a passer-by think falling into people wearing wetsuits on mountains, alpinism helmets, harnesses, knives, carabiners and other iron devices? The peculiarity of this activity makes the outfit really heterogeneous:

wetsuit: shelters from the cold, can be replaced by spealeology overalls and water-tight sailing wetsuit
harness: allows rope manouvres in order to descend the falls. Its use is tied to the employment of carabiners, figure-8 descenders and other belay devices
helmet: sometimes rocks can fall into the river bed...
whistle: falls are noisy, you'll have to communicate...

shoes: usually trekking, spelaeology or gym shoes; canyoning specific shoes are also available
ropes: canyoning low stretch ropes, diameter 9 - 10 mm
knife: to cut the rope in case of need (better once on the ground!)
bolts equipment: contains a hammer and some spits to be used during an exploration or in emergency situations