Disease tracks
I could see myself using these as well.
I think I want to give 5e a fair chance to prove itself, /and/ I'm running for Encounters, so there are some additional guidelines to adhere to, as well. So, I'm not planning on anything radical. I think it lends itself to the style of AD&D, though, so I do suspect there'll be a lot of interpretation and rulings based on player descriptions of PC actions and so forth.I know that a new edition is not going to be able to cover all the bases. As such, I have a suspicion I am going to be retaining a thing or two...
What for you is a must keep from your favorite previous edition, retro clone or parallel game?

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.