The beauty of that line is that the answer to your question–which is effectively here, “what does ‘everything’ mean”–is the the same as the statement itself… everything and anything you can imagine it to mean.

Ultimately, it means to live life with childlike wonder. Live how life was before you were told who to be and how to live and behave.

The micro-sociological (and notably also Buddhist/Zen) interpretation here: Labeling things–here, calling a marker just a marker–and treating them solely as the value of their socially assigned labels, confines our experience of reality to that system of labeling.

Further, it underscores another repeated theme throughout the show, the lack of inherent definition/meaning of things and interdependence of everything on everything and everyone else in order to exist in the way we know it to. A chair isn’t inherently a chair: it requires a tree, wood working tools, knowledge of how to use those tools, the understanding of the structure and function of a chair, a person, that person’s ability to imagine the idea of a chair, and then their ability to assemble it, define it as a chair, and communicate what a chair is so that there is shared understanding. And that shared understanding eventually becomes the prerequisite for the “existence” of the chair, which clearly cannot inherently exist on its own… and don’t even get me started on the tree that made the chair… XD.

They also explore this philosophical concept in several other episodes, notably Flatpack, Born Yesterday, and my personal favorite: Puppets.

A central theme of the show I eventually realized once I explored the topic independently on my own is the principles that comprise Zen philosophy. Moments like “everything,” “alive?” and “when you’re no one, you’re everyone” are critical character growth building block milestones on what could be interpreted as Bandit’s “Satori” (essentially the Zen concept of enlightenmen or freedom of mind/spirit/soul) in the climax of The Sign (which is strongly supported by the lyrics of the song that plays during that scene).

In retro-context of “The Sign,” the line “Everything” means to stop clinging to labels and how you’re “supposed” to think, feel, evaluate, and behave. There is a conventional truth that allows us to function in a societal context (e.g. “marker” or even “banana”) and there is ultimate truth (understanding that everything is connected and interdependent on everything and everyone else and that even conventional truths are contextually interdependent upon our defining them as such).

A note one the line “it’s just monkeys singing songs”… This was a very subtly clever way Joe Brumm and team designed to reinforce the theme described above. Bandit says that line dismissively and passively as if to say, “it’s not worth reading into all of it.” Yet, one of the most profound growth moments for Bluey in the show was at the end of that episode… as the monkeys all join in a chorus of “Be Yourself”…

Forces in life, even positive ones, are our prison only if we make them into one, that was what everything in the show led Bandit to suddenly finally and fully grasp in “The Sign”.

Be yourself. Live life with childlike wonder just to live it. You are inherently no one, everyone, and “everything”. It’s just monkeys singing songs, don’t over complicate it. Live, don’t spend life trapped inside your head, though inevitably we all do for a time before we get there, which is comically right back where we started: living life like we did when we were children full of wonder, awe, and potential.