Not knowing you or the speeds with which you ride at the track, this will all be sort of a guessing game...
Cutting weight for the track all depends on how serious you are about riding the track. If you are a casual track rider, meaning that you don't go all that often, you would be far better served to spend money on tires and track time followed by suspension upgrades rather than trying to cut a few pounds.
However, the quickest weight reduction can be had by replacing the stock exhaust with a slip on or a full titanium exhaust. Then race glass and the removal of all lights as Will already mentioned. You can also save some weight by removing such things as the Secondary Air Injection, Evap Canister, Intake Flapper Valve and Actuator, Idle Stepper Motor, Catalytic Converter and the Exup Valve. Most of these things will require the Race ECM and Race Harness to avoid having the Mil Light illuminate on the instrument panel.
I've done all of these things to my track bike, but by far the biggest gains came from installing 20mm GP Suspension Cartridges in the front forks and installing the Ohlins triple clicker rear shock, oh and the slicks...
I am still running the Triumph TOR Exhaust on both my street bike and my track bike. At some point in time I plan to add the Arrow Stage 2 exhaust and that will shave quite a bit of weight.
Also, Jardine only makes a slip-on for the 675...
Remus and Arrow make full exhausts...