What's the best way to hide the bubbles? Caulk? Speckle? More mud? Note: I want to paint very soon and want the easiest solution.
Could be that your mud wasn't mixed well and had settled a bit, leaving excess water on top. A firmer application or a more thorough mix might've helped prevent bubbles.
At any rate, just skim it again, and press firmly using the edge of the blade. If you do it right it won't even need sanding (or maybe just a wipe).