Howdy and welcome!
Some things I think are absolute necessities are;
A basic or better tool kit.
Spare belt
Tire plug and patch kit.
Air compressor (12v or cordless)
And a first aid kit.
Other necessities depend on your particular kind of riding.
If you do much night riding, a Light Bar and other additional lights are pretty high up the list. The stock lighting is basically adequate.
If you typically ride with a group, radios (Rugged, PCI, Cardo etc…) are extremely useful.
Other items that are useful but not particularly necessary;
I personally like the Milwaukee Packout system. There are a few manufacturers that make Packout mounts for the Xpedition, and then you can do a combination of tool boxes and coolers without having to strap stuff down.
Cordless blower. Super handy for dusting off whatever gets dusty
Clutch kit and/or ECU tune. The ‘25 models already come with Polaris’ “Comfort” clutch, but it’s just heavier weights in the primary clutch. The secondary clutch still has the fairly open helix that can be a little noisy.
A clutch kit from Aftermarket Assassins, Gilomen and others will include a tighter helix in the secondary clutch and stronger springs for both primary and secondary clutches to reduce belt slippage. Then the primary clutch weights can be loaded up if you prefer lower rpms, or you can go for performance with an ECU Tune and lightening the primary weights. Again, this isn’t necessary but can help fit the machine to your needs.
Larger tires. 32” and some brand’s 33” tires will fit without rubbing on up to a 5/2 offset wheel. Also a deeper offset wheel than the stock 6/1 will give a little wider stance for improved stability and a little softer ride.