Well, here's the first. You must have Jaheria in your party for a long time for this to work. Quite a while after dealing with the Harpers in Atkatha, and after a couple of run-ins with Dermin, Jaheria will leave your party while sleeping in the wilderness (ie outside a tavern). Anyhow, when you wake up, she'll have disappeared and a character named Terminsel will walk up to your party and deliver a note from her to you. Now here's the trick, have a thief or bard with high pickpocketing skills quickly pickpocket him twice (boots of speed help). They'll nab a necklace of protection +1 (big deal) and a ring of protection +2 (that's better) from him. Even if they fail the pickpocket try, he'll never go hostile and they can just keep trying. A few weeks later (one walkthrough said it could take up to 3 months of game time!) Terminsel will pay another visit to your party and this time ask Jaheria if what she did (kill Galvery and follow you) was the right thing to do. She'll say "yes" and he'll give her a nifty little amulet. Pickpocket him twice again and you get another necklace +1 and ring +2!
The second trick is handy if you want to take some of that Drow equipment with you to the surface without having it turn to dust. Not that it's the best equipment you'll come across, but the Drow crossbow of speed +3 is pretty nice, especially for Jan. And the chain mail that mages can wear which reduces casting time by 1 is pretty good too. So here's how you keep it. Before you come out of the Underdark, hand off the Drow equipment you want to keep to one NPC (I used Jaheria). Now, kick them out of the group by reforming your party, exit the Underdark and meet up with them in Atkatha. They'll have your Drow equipment in mint condition!
Of course, you could reproduce these results with Shadowkeeper or cheat codes, but where's the fun in that?