My MC's just kind of walking around

If these adventures don't really build on the overall story then why have them in the book? At the beginning of a book you are making promises to the reader and setting up expectations, whether you want to or not. Readers will infer things and expect things to matter, expect the time they spent reading those initial chapters/adventures to matter. If they don't, after all is said and done, many will probably wonder what the point of the beginning was. Some may even get a bit peeved and book may go a flyin'.

If you want to keep the first bit, then make them matter, and give your character a goal within them. Otherwise, why not just introduce that character later on in the book?

 

I have to ask why is the MC behaving in this way? Do you have some reason for it?

I'm also trying to picture how this works. MC has Adventure A. It ends. He has killed a monster or gained some treasure. He's standing there, bloody sword in hand (I know I'm doing tropes) and he says, "whelp, guess I'll just wander on."

Or, he's on the road to Samarra and out jumps a monster! Kills it, wins treasure, then returns to the road to Samarra. Is it more like that?

 

The way I'm reading it, it sounds as if you have a story with a kind of a pause in it. It begins, and things happen that move the story forward. Then at some point in the middle there's a bit of a break, and the main story stops moving forward while the hero goes around and has some unrelated adventures. After a while of this, the main story picks up again and continues on until the end of the story.

If that's the case, I think it may be a good idea to re-evaluate that.
If that's not the case, I've misunderstood the question and you can disregard my comments.

When writing a story, you have complete control over what you put into it, and the reader knows this. I think that on some level readers expect you to have a reason for putting in the things you do, and I think they trust you not to just add in random things for no reason.

I think that if you add in adventures that don't contribute in a meaningful way to the overall story then the reader might feel a bit cheated, and that's not so cool.
That said, it may not be too difficult to add some meaning to these adventures. If they don't contribute to the overall story, there's not too much to be lost on changing them. You could add in parts that lets you explore the character in more detail, or show off the intricacies of the world, or something like that. They don't have to be unrelated adventures.

 

I'm not sure I would be okay with it. If you presented the book as a series of short stories it might be okay, so long as each short story had its own beginning, middle, end, and arcs. But if you presented it as a novel I would expect the premise (and promise) to stay consistent throughout, otherwise I would wonder what the heck the point was.

 

Yeah, based on that info I'd wonder why he was the mc in the first place. Why not pick one of the other guys who actually has a purpose and a goal and a plot to be mc and make this guy a side character? As a reader I would have a huge issue with this.

When I start a book I immediately start looking for the "premise" or the "hook". It is presented as a question in my mind:

Will this little Hobbit get the ring back to Mordor in time?
Will this farm boy be able to save his home from the evil Empire and achieve his dream of becoming a Jedi?
Will this cute blacksmith be able to rescue his love, who has been taken by pirates, and win her hand?

You get the idea. The premise is usually presented early on with the inciting moment:

The hobbit is asked to take the ring.
The farm boy is forced to join up with the Jedi
The blacksmith's love is taken by pirates.

Then the whole point of the book is them solving that problem or accomplishing that goal while obstacles come in their way.

If a book presented a character with a mini story and screamed "this is the main character!" I would wonder what the goal was. What the premise was. If near the end that hadn't been achieved and the character started wandering around aimlessly with no clear direction I would wonder what the heck was going on. If the goal was never achieved I would think it was an enormous waste of my time and emotional commitment.

 

This is really problematic. It sounds like you have a string of semi related mini plots, or events, but no actual story.

 

So, once he gets to that city, *then* what happens?

All this:
You could think of him as a sort of an immortal wandering priest whose job is to give last rights to the dead and dying and to preform exorcisms. He never lingers in one place too long because 1) he's a hold-over from an older religion and the new dominant religion doesn't want him around 2) attachments are forbidden to him so he can't risk staying in any one place too long.

is backstory. Even so, there are two very strong driving forces here. One, the Powers That Be, want him not to Be. So there is a power that seeks to thwart him. Two, he cannot form attachments. Forbidden? I dunno about that, since his religion is on the outs, so may not have the power to enforce that rule. But if it's a kind of personal vow, that becomes interesting. Does he refuse attachments because of some tragedy? Or some ideal?

Either way, the fact that he's now entangled with someone (in the city) means he has to figure out what now. Does he go all in with his new friends? Does he keep letting them down because of that stupid oath? Does he fall in love despite all? Plenty of potential there.

I wonder if your sense of the MC just wandering around has more to do with the author wandering around in the story. Perhaps the connection is not yet strong enough with your MC. I know this happens to me. When I think the story is losing steam, it nearly always means I'm losing connection with the characters. I have to back myself up, get closer to the characters and to the specific situation, make it more real to myself. Sometimes that results in renewed enthusiasm, sometimes it results in loud curses and a major rewrite. And sometimes, I have to confess, it results in crickets. Not often, but sometimes. Then you can usually hear the sound of weeping.

 

What if they're not unrelated? What if there's something more to them that neither you nor your MC know of - yet?

I don't know if you outline or not, or if you do it a lot or just a little, but see what happens if you do. Iterate on the events. Go over them very roughly first, and then do it again, but in a little more detail, and then again with even more detail. Who knows what might show up as you keep scratching on the surface.

 

Again, as a reader I would read the first few chapters and assume that character presented to me was the main character, and that those goals were the story goals. If suddenly, a third of the way through it changed to a new character with new story goals I would wonder what the point was of the earlier chapters and I would feel cheated, again, of my time and emotional investment.

The first third of the story, if it does not include your MC, is backstory then. I would find a way to start the story with how the MC gets involved, or reconsider him as an MC.