DMG Appendices II & III: The Wonderful World of Magic Items
I think even if they don't own it, most long time players are intimately familiar with the contents of these appendices. At low levels, everyone hopes for some random rolls because chances are, there will be some higher level toys generated, and at higher levels, everyone hopes the DM decides to just use a more level appropriate item instead.
There's only one major optional rule in this section, and that governs the use of command words. Yup, what a lot of DMs irritated you with back in 2nd edition's heyday was an optional rule. Beyond this, there are a fair number of "little" rules that a lot of people overlook(and which really should have gone on a DM's screen.
The Potion Compatibility table is just one example. Yes, sorry to tell you this, but if you chug down more than one healing potion in a single turn, by the book, there's a chance you've actually created and ingested a lethal poison.
Next is spell scrolls. Thieves aren't the only ones who take a risk when using these things. If a wizard or cleric attempts to cast a higher level spell than what they'd normally be able to cast because they're using a scroll, then there's a chance(depending on level) as to whether the scroll will fail or backfire. Keep that in mind when you find a Scroll of Wish at 1st level!
The last major overlooked rule is Armor sizing. Magical armor only re-sizes but so much, and comes in only a few sizes. The sizes are: Human(65%), Elven(20%), Dwarf(10%), Halfling/Gnome(5%). Elven chainmail has its own sizing chart. That means your desire to play a Hill Giant Fighter means you'll have to wait until the party Mage or Cleric is level 11+ before you get any sort of magic protections. Either that or you're going to have to go graverob a long dead giant.
Next time: Final Notes