Assuming that your enduro courses are somewhat like thoes on the US, you will need to cut your handle bars down to 28-30" so that it will fit between the trees a little better. Get some stout hadguards - Cycra ProBends are my favorite. While you are at it, make sure you have good strong handle bars as you will likely drop the bike a couple of times in a race - pro-tapers are my favorite.
If its a rocky area get a full coverage skid plate and pipe guard (e-line carbon fiber is my favorite, it offers better protection than any other option, looks trick and doesn't weigh very much).
Make sure the bike is properly jetter, the air filter is clean, you have a well marked fuel can set aside for pit stops. A spare set of goggles and gloves is a good idea too.
Set up the suspension for the conditions, typically you will need it much softer than for general trail riding or mx, due to the tight technical nature of enduros.
Carry basic tools, a spare plug or two, safty wire and ductape in case you break down or need to do a little crash repair - I typically wear a medium sized butt back.
Wear a hydration system - I use a 72oz camel back under my chest protector.
Fresh tires and heavy duty tubes are good - typically you'll need soft terrian tires due to mud and slow speeds.
Many enduros require lights and some even require full street legal set-ups.
An enduro computer or at least roll chart holder and odometer would be handy for timekeeping. Absent these items, find an experenced person of a similar skill level to yourself and follow him/her.
Personally, I don't like flywheel weights on 125's, makes them rev too slowly when you hit the clutch IMHO.
good luck and have fun:)