Essentials:

Wetsuit: everyone entering the water must wear a wetsuit (both long or short-sleeves/legs are fine).
If you are being towed in a vessel (dinghy, canoe, inflatable, etc.) & do not plan to enter the water at any point, you do not need a wetsuit, but will need to bring a well-fitted life jacket/buoyancy aid to wear.
Swim cap (provided by us): we'll give you a colour-coded cap at registration on the day.
Goggles: highly recommended.
EITHER: clothes for next stage/s (to be worn under wetsuit) if you are doing more than the swim stage. Keep in mind that whatever you wear under your wetsuit you will also be wearing for the cycle & push/run. 
OR: swimming costume or trunks (to be worn under wetsuit). We recommend this if you are only doing the swim stage. 
Towel (or two)

Optional:

Nose clip
Flippers & floats: either/both of these are welcome.
Tether: for visually impaired participants or to help tow Superheroes in vessels.

Essentials:

Helmet
Spares & tools in case of flat

Your vehicle of choice:

(Wheelchairs welcome for this stage too)

Bicycle: with or without trailers/chariots & the like to push/pull your Superheroes along.
Tricycle
Handcycle
Tandem
Recumbent bike
Race runner
Wheelchair bike
Wheelchair: day, racing or powered

Some super suggestions:

Comfy running shoes
Wheelchair: day, racing or powered
Race runner/petra running bike
Walker/walking frame
Walking stick
Crutches

(Don't forget any tools or spares!)

Highly recommended

Cycle helmet if self-propelling/being pushed at speed.

Also welcome

Buggies/pushchairs: if you are pushing a Superhero around the course.

Tether: used around wrist