ok man, here's a long one, so walk with me.
Really, you need to either get into the 790/890 whatever Facebook group is most widely used, or join here, and start reading:
https://advrider.com/f/forums/parall...d-790-890.106/
One of the advrider goons curates this too:
https://790adventure.net/ which is sort of a database...things like how to reset the service light, all the little niggles that were part of the 790 launch, anything noteworthy he's been adding. I've no idea if he or someone will incorporate or make a different one for the 890 as some things are different, but they're pretty close to the same bike.
so...get ready to break out your wallet...
things I can advocate for:
a side stand foot. I used some amazon or eBay knock off.
folding clutch and brake levers, same...the brake plunger took a little fiddling with to get it seated properly so it didn't drag, but once it set up, all good.
prerunmoto rear top rack plate
https://www.perunmoto.com/collection...p-luggage-rack
they make some soft luggage stand offs that take the place of the aft/side plastics too, take a gander.
camel adventures 1-finger clutch arm
https://camel-adv.com/collections/kt...bundle-save-25
thats a link to their kit, but you want a headlight support thing before you start getting too sendy with it. you do NOT want to crack those bolts off. put a headlight support near the very top of your list. the heat shield might not be necessary, especially if you do a cat delete (arrow seems to be the best bang/buck if thats your thing), but the 1 finger clutch is a great cheap upgrade, even though the 890 has a different clutch than the 790.
riser/steering damper mount:
https://www.tripleclampmoto.com/coll...-890-adventure
the stock one is similar to a mid 00's gsxr, not great for off-road. a proper damper like this is more of a luxury item, but once you have one, you'll want one on every woods bike.
TCM also makes a headlight brace (which I have), its fine. pick one.
These dudes are on the forefront of performance upgrades:
https://www.rottweilerperformance.co...890-adventure/ high end stuff. but they sell most of the other things you need too, like that skid plate. look at the vanache countershaft guard, Rottweiler fuel pump guard and fuel line elbow replacement, canister removal kit (you dont want the overflow on top of the header), their kickstand sensor relocator, and they make a tail tidy thats nice if that tickles you too. A single disk conversion is probably next on my personal list after I get my suspension worked, ala 950se style, but with better components (the 790 is already ahead here with a more powerful stock master than the SE had, but the Brembo stuff is sexy, as we all know).
I use whatever amazon style grip heater kits are out there that dont use a big ceramic resistor for the low setting. I like the hi/lo filaments in the bar wrap itself. the factory grip warmers are cumbersome, and the grips suck (so now I can run the pillow top dirtybike grips too), and it cost 3x more anyways. same thing with the seat heater. I used a kit, and installed it under the seat cover myself.
my bike currently has a seat concepts seat on it, and it works better for me than stock, but I'm not married to it. they do make a few different shapes and heights though.
tires and wheels: tires are for you to pick, but the stock rims are notoriously soft. they'll ding. if you ding them hard enough you run the very real risk of flatting, as they're tubeless. It'll cost about 750ish to strip the wheels to the hubs, ship them to dubya, and have them built to suit, tubed or tubeless, and you can still use hem bearings or your standard upgrades from all balls. its also 500ish cheaper than the power parts wheels or a complete set from one of the aftermarket companies. the stock wheels are serviceable, dont be too scared to ride the bike, but do count on putting a few good whacks in especially the front as you grow into it. for whatever reason, they unnecessarily wide as well, which was another reason to get them relaced, but mostly just cuz they're made of butter.
when it's time to do chain and sprockets ill drop a BRP chain slider on too, so I'm less likely to bend those mounts on the swingarm.
skid plate and bark busters we covered, with fold away mirrors (I use the universal ram ball style), I use a quad lock phone mount too for the bars...they now make an anti vibe thing to not kill the phones camera (which I've not experienced), but I have the old style thats more rigid.
when I did the canister delete I heat shielded the inside of the fuel tank, put the Rottweiler pump guard/elbow on, and a powercell fuel cap replacement. the latter is not necessary, but the stock cap becomes a little annoying with the steering damper in the way.
luggage. pick a system. Mosko offers a set of offset (so you can put the thinner one on the exhaust side) and their own pannier rack, that together is more or less the same price as the bumot rack and soft panniers. if I were only using soft bags, I'd go with the Mosko, personally. I like the hard bags for the shelf it creates, as I mentioned earlier. the bumot soft bags have a rigid back and mount to the racks solid, but the Mosko stuff is much more modular, if you were going to expand or add on for a longer trip.
I have one of the duffels that twisted throttle sells too, I think its a dryspec, which isn't so bad, but I've heard they're prone to ripping the mounting straps off in real fast woodsy conditions.
time will tell. wolf man, giant loop, Mosko, and maybe a few others make adv spec soft luggage. it's a buyers' market.
I may think of a few things I missed. I intentionally left out performance stuff, intake, exhaust, fueling, and the like. some people automatically toss a loud can on a bike first thing. I'm not one of those characters. especially with something like this, I quite like to sneak in and out of places with no notice. a loud exhaust defeats that purpose. also, the tc on the bikes chops the throttle in wheelspin situation, so getting this bike to make more power seems silly, especially when you consider this very simple thing: any adventure bike will spin the back tire in any off-road scenario. so making more power here is a waste once the tire is already broken loose.