What items should be saved for turn-ins?
In Fallout 3, Pre-War Books, Scrap Metal, and Nuka Cola Quantum (among other items) were all far more valuable when turned into specific NPC's, rather than just sold to whichever trader you came across first.
In Fallout: New Vegas, are any of the same items, or any new ones, worth holding onto for a larger payday?
I've made this community wiki so that more people can edit it and we can simply have one definitive answer. In doing so, I've also incorporated answers not only from what I've found via gameplay and The Vault, but also the other answers which are on this question as well.
- Sarah Weintraub: Various Vault Jumpsuits, but not armored ones nor utility suits.
- Festus: Sunset Sarsaparilla Star Bottle Caps (sort of -- with 50, he, sort of, gives you the "reward" of hearing the history of Sunset Sarsaparilla and a quest for the "real" reward.)
- Jane (Lucky 38): Snow Globes (the spiritual successors of Bobbleheads from Fallout 3, but do not grant any bonuses)
- Raquel (Boomers): Missiles (thank you Brian Schkerke)
- Jack (Boomers): Scrap Metal (thank you Douglas Leeder)
- Julie Farkas: Fixer, RadAway, Med-X
- Decanus Severus: NCR Dog Tags
- Quartermaster Mayes: NCR Dog Tags
- Private Sexton: Legion Ears
- Lindsay (Boomers): Mr. Cuddles (unique item)
- Ruby Nash: Radscorpion poison glands (traded for Ruby's Casserole)
- Isaac: 100 scrap metal, tin cans, bent tin cans, pots, coffee pots, metal cooking pans, metal cooking pots and/or irons
- Jas Wilkins: 1 deathclaw egg
- Children near Nellis Hangars: Rocket Souvenirs (though you only get Boomer fame, no caps nor other rewards)
- First Sergeant Astor: Irradiated NCR Dog Tags
You can give scrap metal to Jack (Boomers) in return for Boomer reputation.
Raquel (Boomers) wants missiles, stating that they have less than five years worth of missiles for their launchers.