So, I've reached the game finale, but am severely underpowered for the boss fight. The cultists that are guarding the ritual room are all packing high-level weapons and I've walked through all of the bunkers with an SKS in my hands. My companions aren't equipped any better and I'm still level 11 despite having run out of available quests. So, how do I get there? How do I level up and get better gear? Do I just randomly travel the wasteland in search of experience points or did I miss something?

Here the video with the final fights on expert.

https://www.youtube.com/watch?v=7r7E0z9khv8

Somewhat hilariously (and I suspect unintentionally), it's possible to bypass all fights (as well as all dialogue) in this entire bunker by munching a mushroom and then just casually strolling past everyone...

Um... a mushroom? Do you mean fly agaric? I'll try that for sure, but I would still like to finish the game legitimately. Seems like it's back to the wasteland to hunt raiders for me then...

In the English version it's "Amanita", but yeah that's probably the one. Haven't done this myself, but saw a video where someone did: https://youtu.be/LUfGJql8Y8s

What are your stats? I smoked a few joints and put on some cologne (IIRC my personality was 5 before buffs) - that can get you past the first group.

The second (and final) group, it is possible to convince the main guy to see things your way - I think it requires high intelligence and/or speech. After passing that one the speech way, I reloaded and decided to wipe them out instead - killed the main baddie with a single shot to the eyes. I did have the crazy experimental weapon though (where you only find 7 bullets or so in the entire game) - I got it from one of the bunkers, can't recall which one. The doggie got killed in that fight, while only one of my other chars contributed since he blocked the door so no one else could get a shot in.

I think I was around level 15 by that stage though, so you might want to check what stuff you've missed - I rarely engaged most enemies and got there primarily via quests.

Thanks for the tips. I'm pretty sure that I've been to all of the locations and completed almost all of the quests that the game provided and still was level 11. Guess I didn't fight enough. Which I do now. And traders have their stocks updated according to my level, because I've just gotten my hands on a Remington rifle. Good times. However, the situation that I got myself into in the first place suggests that the game needs more content. And I'm glad to hear that the developers are working on a DLC right now.

Well I didn't go out of my way to fight anything, and in fact avoided a lot of fights - near the start, because I'd get my ass whooped, and near the end because I was rich enough and well equipped enough and couldn't be bothered.

Did you talk to every single NPC in the game? There are tons of quests that are easy to miss, and there are a fair few XP to get just from talking to people and discovering something unusual/secret (which often requires a stat and/or skill check). There are a fair few quests which you can easily miss altogether if you don't meet the stat/skill requirements - like the Death Gang for example (which you'd know if you've done this quest, since you'd have a unique helmet from it).

I agree the game needs more content though - those two extra maps are almost entirely empty.

Are traders really tied to level? Which could possibly explain why I never found a single weapon that could fire the 14.7mm ammo (despite actually having a reasonable amount of this ammo).