Some stuff I do:
Arnold Dumbbell presses
Push-ups (these have helped me tremendously)
Lat pull-downs
Cable rows
Dumbbell flyes/flies
Decline bench press
Pull-ups/assisted pull-ups
Dumbbell raises to the side and then again to the front

ETA: when I do stuff that targets the chest (flyes, decline bench, etc.), I do them after I complete workout A. My reasoning is that I want to get through SL as written before I do anything extra.

Big fan of push-ups (normal, hand release, plyo, decline), pike presses (handstand push-up progression), recline/reverse/bodyweight rows, pull-ups progressions, and anything bodyweight really

If you wanna do DBs or KBs, 1-arm snatches, power cleans (or squat cleans for a full body beat-down), presses/push press/thrusters(again, full body funsies!), bent-over rows are quite effective. 1-arm chest press are pretty interesting, too Incline bench is a good one.

If you wanna do cables, triceps push-downs and face pulls are pretty good accessories.

It does depends what your goals are. The best accessory I've found to help OHP was the bottoms up KB press. You'll use a lot less weight, but it'll bring up your stabilizers something wicked (if you don't have access to KBs, an hex dumbbell might work, but it won't be quite as effective)

I'm still tweaking mine and they will probably change some as I have 3 different sets of accessories but stage 2 involves a couple of them in NROLFW so I'll find new ones.

On the day that is arm specific I do bench, dumbbell bench, sometimes bicep curls (but i don't understand those and still can't figure out the ez curl bar) and wrist curls. I do a shoulder type day that includes shrugs, assisted chin-up (sorta, i'm short so not quite reach to my chin), front squat and overhead press. I do pushups as warmups many days and one of the days in stage 1 required pushups so there was that help along with seated row, lat pulldown and seated db overhead press as part of the actual program.

Not a whole lot and some of them are lifts I liked in SL and missed during stage 1 of the other program.

For stage 2, which is just 8 workouts, I'll have to replace my front squat/ohp as the workout A has front squat/push press. I'm also looking at more ideas for forearm wrist because it's a weak area of mine, along with just general upper body. Will plan things more before I start that in April.