The prizes that you can win for taking first place vary depending on the class that you are racing in. There are four classes: C, B, A, and S. Every Chocobo starts out as a class C racer and with every three first place wins, your racing class will be increased. Obviously the lower the class, the less items you can win. Here is a list of items broken down by what class they are available in and how much GP they are worth, in case you want to exchange them for GP instead of taking the item. X means it is available in the specified class and a blank spot means that it is not availalbe:

Item Name	GP Value	Class C	Class B	Class A	Class S
Antarctic Wind	20	X	X	X	X
Bolt Plume	20	X	X	X	X
Cat's Bell	500			X	X
Chocobraclet	400				X
Counter	300			X	X
Elixir	200		X	X	X
Enemy Away	300		X	X	X
Ether	30		X	X	X
Fire Fang	20	X	X	X	X
Fire Veil	50			X	X
Hero Drink	15		X	X	X
Hi Potion	15		X	X	X
Hyper	10	X	X	X	X
Ice Crystal	50			X	X
Magic Counter	500				X
Megalixir	300				X
Phoenix Down	10	X	X	X	X
Potion	5	X	X	X	X
Precious Watch	300				X
Sneak Attack	300			X	X
Sprint Shoes	500			X	X
Swift Bolt	50			X	X
Tranqilizer	10	X	X	X	X
Turbo Ether	150		X	X	X