Fillin’ the downtime.
Here’s the thing: If it’s ‘fill’ with no other purpose, it’s got no right to be in your story and you’re gonna cut it later. If you need time to arrange places and characters and let things stew in your head, go ahead and write the extra, and trim it as you revise.
However, it sounds like you are having trouble getting the non-plot point stuff in place to begin with, so let’s work on stuff that you won’t need to cut later while we’re at it.
‘Fill’ to me means ‘fluff’, ‘superfluous’- in other words, it has no point.
Instead, let’s refer to the lulls between plot points as ‘downtime’. This means all the stuff that the characters are doing when they’re not fighting monsters/betraying each other/committing regicide.
Before you write downtime, figure out what you want to convey to your audience with this scene- in other words, your point for having it in the story. You could show the relationship between two characters. You could foreshadow future action. You could show a change in behavior that is a result or lead up to a plot point (OUT, damn spot!).
Pick out something that you haven’t shown well or developed enough in your writing, or something that you can’t show as easily in the plot uptime. Then write a scene that’s got threads of that woven all through it.