I allow most of the PH, some other material from e.g. Volo's et al, and a ton of homebrew.
Drow are not pcs in my game, nor are many of the random added races. Most class material (but not all- no obviously broken stuff like Twilight cleric, spells like healing spirit, etc) gets in. Feats, usually, unless they strain my credulity (Poisoner, I'm looking at you, and I still haven't decided whether to allow you).
Depending on where you are in the setting, you may have some options that aren't available elsewhere.
I'm basically extremely strict about anything that I find unbalanced compared to the core rules, anything that doesn't fit the setting, or anything that I feel doesn't fit the setting here, but it might fit in sometime over there.