After you buy the three core books (or just the PHB, if you’re just a player), what do I recommend next? Well, here is a list of books. I’m trying to have them indeed in order, not just of immediate purchase order, but of long term significance, and how useful it is in a system agnostic fashion.
I’m not including the content of Adventures in this list, but if an adventure has a useful table, then i’ll mention it here.
0. Xanathar’s Guide to Everything (5e)
I think I might mentally count this as a core book, and not an add-on. I recommend this over the DMG, actually. It’s a great resource for how to do things in 5e. A combination PHB 1.5 and DMG 1.5, it’s a good purchase for DM’s and Players. I don’t think it’ll have much legs past 5e, but right now, it’s essential.
1. Acquisitions Incorporated (5e)
I love the Acq-Inc book, for surprisingly small reasons. This is one of the few books that changes the tone of D&D, the others all being about horror. This bring office comedy into D&D. In addition to the company roles, which are a neat idea and may have kept me from making the Specialty system if they had been released earlier, they do a lot of stuff with downtime that fixes and provides options for things the other books were missing. It’s a crucial step in understanding how to use downtime.
2. Volo’s Guide to Monsters (5e)
While most of Volo’s is a Monster Manual, there’s a bit for players that’s nice. The coolest part of the monsterous races in Volo’s is they have quirks that make them easier to play as a true non-human. And that’s fun. The real value of this book though is the first 100 pages, which elaborate on a handful of monstrous factions, giving a GM plenty of ideas of how to work them into your game.
3. Arms and Equipment Guide (3e)
Saltmarsh Chapter 1
Descent into Avernus Appendix Demon Bargains
More will obviously added later. Please ask about specific books.