Going tubeless is a good move. No idea what your stock tubes weigh, but considering what a lot of fat bikes run as standard, you could save some serious weight for very little money.
edit: A single stock tube! Plenty of other people have success using cheap Q-Tubes weighing about 250 grams each. Just swapping to those tubes could save close to 700 grams!
A brake upgrade also sound like a good move. If you've got the budget, a switch to Formula R1 can save decent amounts of weight (as would XTR and a few other brands). For a low budget alternative, see if you can get a good deal on low/mid level Magura - they're surprisingly light compared to other brakes in the price range. Even if you don't change the brakes at this stage, KCNC/Ashima rotors will save some weight and be pretty cost effective. If you can find some light, alloy backed pads for your existing brakes, you should also get a decent saving there.
e*thirteen make a spider/ring that would save some weight if you decide to switch to 1x10. The direct mount style FD's aren't exactly light and you get to ditch a shifter so it's a worthwhile saving if you can live with the reduced gear range.
Just the usual
stuff other than that.
Lighter cassette - I imagine the stock cassette is pretty heavy. A good saving with something like an XG-1080 cassette.
Post/bars/stem - Mt Zoom bars are an example. Even some eBay carbon. KCNC have some good alloy options. Uno stems are great value for money etc.
Foam grips, fork expander, seat clamp etc - cheap places to save a few grams.
Maybe a bit of bolt tuning too?