1) Two Motors ( I used these Plastic geared motors http://www.nex-robotics.com/index.php?page=shop.product_details&flypage=flypage.tpl&product_id=536&category_id=13&option=com_virtuemart&Itemid=45
2) Nylon Rods or Aluminium Rods ( Aluminium preferably -- learnt it the hard way! I've used nylon rods, yeah they are quite light weight but are really difficult to machine whereas aluminium rods are light as well as easy to machine)
3) Acrylic sheet ( I used this, you may use any light weight material you want. I used this because i)Light weight ii)Can be easily cut into desired shapes iii)its transparent look looks good!)
4) Some wires(for motors)
6) O-rings( Diameter of whose is around 1-1.5mm less than diameter of your motor shaft )
7) M-seal and Feviquick
8) If you are going to cut the acrylic sheet at home you might need a tool such as Glass cutter. Its very cheap. Costs around 15-20 Rupees. You can get this in any Hardware shop.
9) Two empty cans ( for buoyancy!)