Modoc is a small (and dieing) farming community right between the Den and Vault City. You may stop here for a couple of small quests, if you want to, but unless you did hear Karl's story in the Den, I'd advise against starting the main quest (the haunted farm one) yet. It ends up with you having to go for Karl at the Den, and with a very tight time limit at that. You can take it on the way back from Vault City, when you return to the Den with the fuel cell controller for the car. That's where I'll talk about it, anyway, so skip a few pages down if you did talk to Karl already and you want to do it now.
You can have a rural style shotgun wedding here, if you seduce the
butcher's daughter or son. My favourite was seducing the daughter
with the female character. I sure had a laugh at that wedding.
Unfortunately, however, either spouse are real lousy party members and
they do NOT level up ever. I.e., they're useless. Me, I'd say just
reload after having the laugh at the wedding.
You can take a quest to guard some brahmin from a large pack of wild
dogs, from the butcher. It pays 1000$ if you don't screw up. Be
warned that although brahmin are pretty robust, the dogs are fast and
many. Hit the "A" key to get into combat mode fast: it gives you a
better chance of moving into position before the dogs get there. Then
move right north of the cattle, and start sniping the dogs. It helps
if you have a better weapon than the lousy 10mm pistol (e.g., if
you've pacified some robbers on the way.) Preferably a hunting rifle,
since it has much better accuracy at long range.
On your way back, you can use your doctor skill (if you have good
doctor skills, that is) on an injured brahmin. You get some xp, and
she starts following you for a while. I've heard that you can sell
her to the butcher, but I never had the heart to do it. Then again,
maybe it's just a rumour.
The tanner asks you to find his boy, but that boils down to the same
haunted farm quest, so you may as well skip it for now.
In the north-east corner, there's Rose's bar. She has a Deathclaw in
her barn as a chicken, and you'll get 100xp if you enter the barn.
Then again, that puts you in combat with the Deathclaw, and for this
moment she's a bit tough. Personally, I'd say just leave the barn
alone. You can enter the brahmin fries eating contest here, but be
warned that you'll get poisoned, and as far as I can tell there's no
xp in it anyway.
A senile bum in the far back room gives you a quest to find his gold
watch. Talk to his friend Farrel. Go out, open the outhouse and go
down. (Yech!) There's a passage blocked by some cave-in. Put an
explosive there, and get the hell out, fast. That means, run for the
ladder. Kablam! Now the outhouse blows and all the area is covered
in crap. Gross, but real funny. Go back down, fight the molerat,
retrieve the watch. (Looks like a box.) Go give the watch to Farrel,
for 1500xp. Alternately, you can give the watch to the senile bum,
and you can either tell him where you found it (and he'll accuse you
that you're the thief) or lie that Farrel is indeed the thief.
Beats me why'd you want to accuse Farrel, except maybe for that warm
fuzzy feeling that you're a son-of-a-bitch :) If you accuse Farrel,
you can no longer do Farrel's quest, if you haven't done it already.
You can also get an easy quest from Farrel, in the house sout-east
of Rose's. Namely, you have to kill all rats in his garden. I had no
problems killing them unarmed, to save ammo usage.
When you're finished here, leave for the Vault City...