Back on topic: magic item wish lists.
For starters, there are more stat-boosting items in this edition than I expected. For example, Ioun stones give +2 ability. These things presumably stack, although they are limited to max of 24, so that's something.
It's not game-breaking but I noticed that a ring of warmth is strictly better than amring of cold resistance, and also more common. I'm sure there are other quirks like this in the item tables. Probaly some abuse loopholes there if you allow trade in magic items. (Magic item arbitrage?)
Rings of elemental command get cool benefits if you slay an elemental of the matching type. They're legendary items, so by the time you get one it should be no problem to have your caster buddy summon an elemental for your party to gank.
A two-handed finesse weapon can unlock a potentially broken build, because it would allow Great Weapon Fighting Style to stack with Sneak Attack for a pretty nice damage boost. Sun blade is a rare item that can function as a finesse longsword, and can be wielded by anyone with short sword proficiency. It's on table G so there's a 0.03% chance it shows up in a 1st-level treasure hoard. Any min-max rogue would love to get a sun blade, splash a level of fighter to get GWF style, and then go Arcane Trickster and play a Jedi.
(Elven moonblade, a legendary sentient item, also has a small chance to become a finesse longsword.)