I better go retrieve 'Lysander's Cry' Sparrow right now before I forget again and time runs up

Is there anything else important (non purchasables/I don't buy stuff) that will be "going away" for good come reset on Tuesday?

Is it from one of the daily packages at the top of the stairs in the Tower?

Yes. It shows up in your consumables section.

• You will destroy to rebuild
  
  
• An unusual amount of engrams will turn into strange coins.
  
  
• Your enemies will tremble before you
  
  
• Be open to others, your walls will come down.
  
  
• Master Rahool will surprise you. Then he will disappoint you.
  
  
• You are not alone.
  
  
• Listen to the quiet and learn what it has to teach you
  
  
• Shaxx will inevitably shout at you
  
  
• Your future is full of Glimmer, engrams, Strange Coins, and legendary Marks
  
  
• You warm others in the coldest times
  
  
• You will pull off a stunning upset in the Crucible
  
  
• You will achieve your aims through cunning and stealth
  
  
• Your pockets will overflow with Glimmer
  
  
• Listen to the quiet and learn what it has to teach you
  
  
• you will fail to impress eris. but then, so will everyone else
  
  
• The Speaker will dream of beautiful and terrible things
  
  
• You will gain favor in the eyes of the Vanguard.
  
  
• You have much to offer those you meet, and they have much to teach you.
  
  
• you will forget to thank your ghost. Again. Sheesh
  
  
• The world shivers with the sense of change. Anything is possible
  
  
• You will not be forgotten.
  
  
• You are not alone. The Tower stands with you. The City stands behind you, cautiously
  
  
• You stood by the City in its hour of greatest need, and you will do so again
  
  
• When all is lost, you will still be a Guardian, and you will still be enough
  
  
• You will demolish your Sparrow at high speed
  
  
• Help my name is Cayde and I'm stuck writing fortunes in the Tower
  

Neat Stuff. Plus, it gets you the "Dawning Fortunes" Grimoire Card, so get that while the getting's good!