Absolute best accessory out there is a little magazine release extender made by KRG (Massoud here on the site). Keeps you from having to stick your finger into that mag release paddle.
The production version is a bit different from this... but it's the best accessory ever!
In terms of 'factory' accessories, mine is a folder. Never would have spent the $$ on that, but got it at standard price as it was a LEO demo. If you want a folder, get one from KRG. You will love it if you want a folder. Mine has a brake, but it's not something really needed on a .308. Mostly the brake annoys people next to me at schools which is arguably a feature. And I have a factory front tri rail, though I had to customize it by milling away some of the top rail to clear the bell of my scope.
Non Sako accessories... besides the magazine release... an Atlas bipod. I agree that the Sako factory bipod is brilliant, but very pricey. The Atlas has done everything I ever asked of it. My rings are USO and I can't remember whose 20 MOA down base I used. It was not Near... but Near makes a top-notch base. Has USO bubble level. Sling is a nice, quiet, oiled leather $20 H&K military surplus sling with hook mounts. Maybe you can count the sock filled with Beanie-Baby stuffing that is usually tied to the stock with a dummy cord as an accessory, too. Don't leave home without it. And that's... it. Here's a good picture of the rifle taken while on the stress course at a school a couple of years ago.
Best advice with the TRG... spend the up front $$ on ammo, not accessories. Once you shoot it a bunch, you will know what accessories you want/need. But if your goal is to shoot holes in holes, then you don't need any accessories at all. It will do that out of the box.
Congrats on the TRG... you won't be disappointed.
Cheers,
Sirhr