For hairline cracks, I use super thin CA. If there is visible separation, I use Starbond brown medium thickness CA -- it's not really brown, it's a pale amber that works well in most wood species because it looks more like a natural resin canal rather than something fake that I used to fill a crack. If there is a natural void or bark inclusion that needs some repair work, I will sometimes mix coffee grounds with CA or epoxy. It does a nice job of imitating decayed inclusions. I will usually pack some dry grounds on top of the glue to achieve the final effect.
Sometimes out of necessity I use the fast set epoxy, but if I have a choice, I prefer the 60 minute epoxy because it will have less trapped air by the time that it has set.
I turn a lot of mesquite which frequently has ring shake with large gaps. If it is in a location that will cause problems, I will separate the two pieces and use epoxy putty to do some "reconstructive surgery" to replace the missing wood. It's a tedious process mimicking the adjacent wood grain, but it can be convincing.
I tried mixing sanding dust with glue about a dozen years ago because that is what many other turners suggested. When I saw the results, I decided that it was most definitely not to my liking.