My current AD&D campaign is literally nothing more than a series of dungeon crawls. Well, we did sneak in some hex crawling last session. But I'm not even trying to pretend it's anything else. And the PCs have so many social connections. it gets difficult to track.
Initially, there's the mentor/master. This is who the PC will ultimately have to return to for training to level up. Magic-users will generally have their master, clerics have their church, thieves could have a mentor, guild, or gang, and fighters could serve a guild, barracks, or mercenary troupe.
Then almost immediately--for me, after the first adventure since I like to get right to it and don't have much happen before--is you've got your suppliers. Armorer, weaponer, general trader, alchemist/apaothecary/herbalist/witch for the magic-user to re-up spell components but also for stuff like garlic and wolvesbane which might come in handy for any of the adventurers. A lot of times, there will be need to visit the temple for healing, cure disease, and so forth.
That's the initial contacts. Through play, connections can grow quickly. And again, keep in mind I'm doing nothing but dungeon crawls and this stuff comes up in spades. We joke that if either party is surprised, no one wants to give up element of surprise, so there isn't going to be any parlay. But apart from that, assuming there's not a hostile reaction, any creature the PCs can speak with (due to common language), I make an encounter reactions roll. If the result is anything but hostile, I start tracking loyalty. On more than one occasion, PCs have teamed up with a rival adventuring party or even a group of humanoids encountered in a dungeon to take out a common enemy.
If the PCs venture to a different city or town, they have to develop connections with their mentors, guilds, and suppliers there. And unlike initially, where I just assume you've got the stuff you need to get started, for these future connections I again call for encounter reaction rolls and track loyalty.