If I might be so bold: I always thought treating to a huge meal after working so hard to lose the weight seemed - I don't know....self-defeating somehow.
How about treating the winner to something special to them?....for you tri stuff...for her whatever her interest is.
As for a tie - split the reward between you, after all......you BOTH won, enjoy it!! and make it a date to go with each other to spend the reward!
Life should NOT be a journey to the grave with the intention of arriving safely in an attractive and well preserved body, but rather to skid in sideways, champagne in one hand, strawberries in the other, body thoroughly used up, totally worn out and screaming: "Yeah Baby! What a Ride!"