I know Storm King's Thunder isn't out yet, but I think I've found a couple of adventures that would make fun sidequests to throw into the mix.
The first is a new release from the fine folks at Kobold Press called Sanctuary of Belches. While this 5th level adventure is an obvious tie-in with their new 5E Tome of Beasts (which I have and am in love with, more on that later) it's also definitely a nice timed release, considering it's giant themed and Storm King's Thunder comes out in a few days. I've not picked this up yet, so I can't say that it's good, but it sounds interesting and I'm going to.
The second adventure that would make a fine sidetrek for SKT is The Secret Party House of the Hill Giant Playboy, which can be found over at The Dungeon Dozen. This is a fantastic and amusing adventure that's a few years old. Consider I believe the plot of SKT has to do with the divine order of giants being broken, the idea of a hill giant trying to act like a hedonistic human noble actually fits thematically. Even if you aren't running the storyline, you should check this one out. Be advised that it's written for Swords & Wizardry, but converting it to 5e really wouldn't take much work at all.
Finally if you want a little taste of things to come in Storm King's Thunder you should check out Matt Mercer's mini-campaign Force Grey: Giant Hunters. There are only a few episodes and they're relatively short, though immensely entertaining.