Well, I'll have a stab at it, because you asked & im awake. Then wait for those who actually have a GRiSO to chime in later.
The "service kits" seem to be made up by those dealers who end up selling to owners. You'll need -
- Oil for the engine
- oil for for the gearbox & final drive
- oil filter
- air filter
Then it's a good idea to have on hand, in case they are sub-par
- crush washers & o-rings for the drain plugs & the dipstick
- a set of valve cover gaskets
- grease for those bits that need greasing - drive shaft, Uni joint, swing arm bearings.
That should get you by. Check the maintenance tables in the user manual or the pegged topic just above this for the things to be looked at. There's likely to be a GRiSO-specific tutorial on here in the appropriate section - worth consulting - there's others that have gone before.