My favourite Shadowrun Fifth Edition supplement is the Run Faster source book. Run Faster is easily an essential general purpose book, not only because it expands player options but also because it makes character creation easier and, in many ways, a little more fun.
Note that this post is for Shadowrun 5th Edition, even though at the time of this writing 6th Edition has been out for a few years. I haven't switched to 6th Edition, and I'm just writing for what I play (and more importantly, what people I invite to my games can use.)
Run Faster offers two new methods of building characters. The Sum to Ten method is a variation of the standard Core Rulebook method, which I discussed in a previous post. This post covers the point buy method, a drastically different character build process that uses a lump sum of karma points you can spend on character "packs." It's a lot of fun, and I probably won't be able to encapsulate it just by talking about it, but I'm certainly going to give it my best shot.
You know how you get 25 karma to spend during character creation? In the point buy system, you get 800. The catch is, of course, that everything costs karma. There is no Priority table, so you don't get points to spend on special attributes, attributes, or skills. Instead, you buy your metatype on page 64, and then you buy "life modules."
A life module is a bundle of skills derived from your character's lineage (whether you were born and raised in UCAS, CAS, NAN, or Tairngire), formative years (maybe you spent your life in an arcology, or a rural area, or as a street urchin, or in a military school). They grant you attributes and skills and qualities based on archetypal assumptions about your character's life experiences.
Next, you choose what kind of further education your character received. There are life modules for community college, trade school, university, and military school, or none of the above. Then it's on to the rest of your life: maybe you spent time as a corporate drone, a combat correspondent, a drifter, celebrity, political activist, private dick, soldier, merc, ganger, or something else. All of these life experiences add to your skills and attributes, and it all costs karma.
Significantly, Magic/Resonance isn't allotted by any life module, so a magic user build must spend karma on that special attribute, as described on page 107 of the Core Rulebook.
With whatever karma you have left, you can buy contacts and purchase gear. There are over 25 pregenerated contacts starting on page 182. You can use them, or modify them to suit.
Equipment kits start on page 228, and it's a chapter that's easily worth the price of the book. Spend 5 karma, for instance, and get a basic runner pack valued at 10,000 nuyen, containing everything a new-ish Shadowrunner needs. This makes the initial shopping trip as quick and easy as it possibly can be.
Here's the list, followed by the pages you don't have to refer to because you got it as a pack:
There's a cheaper pack for just 2 karma. And there's a lot more than just those. There's the blademaster pack, big boom pistol pack, heavy security pack, an assortment of bioware packs, decker packs, rigger packs, and more.
Sure, it puts your character build on rails, but it also cuts out the scanning through pages and pages of a lot of restricted gear that you can't get yet anyway. Maybe it's because I have an aversion to shopping in real life, but the Pack your kit chapter is one of my several favourite chapters in this book, and I use it even when I'm not using the point buy system.
I find it useful sometimes to check in with a known good character build. Starting on page 160 of Run Faster, there are pregenerated character builds you can either use directly or use as models for your own build. There are archetypes such as a combat medic, investigative reporter, rocker, undercover cop, and more. This in addition to all the sample builds in the Core Rulebook.
There's a lot more in Run Faster, and actually I consider it a must-have Shadowrun supplement. Then again, I don't own that many Shadowrun supplements, so maybe they're all this good. Either way, I use Run Faster almost as much as I use the Core Rulebook, both as a player and GM.