Must have
Paper, pencil, eraser, d4-6-8-10-12-20 dice.
Like to have
Prewritten adventure and notes, PHB, MM, DMG (and/or appropriate/needed reference materials), laptop (for access to SRDs), gaming table with suitable space for everyone's papers/notebooks/dice/and computers, plus room for food and drink (if not individual cupholders), good lighting, space to walk around said table, dry-erase battlemats (possible built in to table) and dry-erase markers for drawing out terrain/areas, mini's are completely optional but enjoyed/do make things easier (especially large numbers of foes or elaborate terrain/multiple foe scenarios).
Would like to have but don't...
I, personally, really don't have anything beyond paper/pencils, a laptop, two sets of dice, base books (albeit for a few different systems and editions), and a laptop (to look things up). Soooo, pretty much all of the above and the addition of a "game room" to put it all in, plus:
Enough seats, preferably individual chairs, with arms that have wide seats and cushioned backs. Nobody crammed into anywhere. Nobody up against a wall. You should feel like you could take a nap if other players are taking too long on their turn.
Ample shelving for the myriad books, binders, and boxes of all imaginable miniatures.
Projector & screen (built into gaming table or not) - holographic (when the technology gets there) would be nice.
Ample outlets and charging ports (preferably built into the table, but ya know, power strips are fine).
A sideboard for laying out snacks/food (large enough to accommodate multiple pizza boxes).
Dedicated fridge within the same room for beverages (and/with ice maker).
I'm sure technology will make something else necessary before too long.