There are a lot less of them in New Vegas than there were in 3. With all of the new crafted items and various needs for many items, it has really made me start thinking about picking up a lot more things. I used to ignore everything that wasn't on my set list of "stuff to loot". Now I pick up everything at least once. 
 
One thing I have found to be quite useless and also superglued to the bottom of your backpack is the Rocket Souvenirs... I have 157 of them for ever. I cannot sell them, drop them, nothing. I would love to have them just sitting on shelves in my homes... But it seems I will have them for life.

they are for a quest 
 
Always pick them up. they are worth caps and weigh nothing

Here's a list of the items used for crafting. Handy for pack rats like myself. 
http://fallout.wikia.com/wiki/Fallout:_New_Vegas_crafting

 they are worth caps and weigh nothing "

Alternatively, there's a way to do the quest in question WITHOUT the rockets.  It's actually, in my opinion, easier to do it that way. (w/o the rockets).
 
Also, they CAN'T be sold.  They're essentially worthless.  But they're weightless, too, so it's a moot point.

" @bwmcmaste: The quest you get from the other guy in the dinosaur will eventually require them. You cant drop of sell them yet until you complete the quest, then you can sell the rest. It doesnt matter how many you have as they weigh nothing "

There's a mod on newvegasnexus.com that sorts your items in the inventory. One of the optional addons to that mod also adds a label to items that are crafting parts. I recommend it to anyone playing the game on pc, just makes your inventory neater..

 I did notice that virtually everything you can pick up now can be used in a crafting recipe. So of course I collected and stashed everything. Of the literally thousands of items I picked up and stored, I think the only crafting recipes I ever used were:
 
- Recycling used energy clips
- I made Party Time Mentats 3x for the charisma boost.
- Healing powder via the quest in Goodsprings
- Made one stimpack after finally finding some of the appropriate root.

Everything else I have saved is useable in crafting recipes, but when in the game do you really need to craft anything? Oh, and since I got the achievement for getting banned from the casinos, I have 60,000+ caps. So, basically, I could craft a ton of borderline-useless stuff and sell it to make even more useless caps. Great.
 
And that's why I'm back playing Fallout 3.

Why are there rock-it-launcher parts, but no rock-it-launcher?

I'm close to 60 hours in and I've been deliberately avoiding the storyline, just scouring the wasteland and improving my character. I've only found 1 schematic thus far. It's pretty cool how many different ways people play this game. At the moment, I'm just trying to clear all the achievements, and stay in everyone's good reputation graces. Well, the Powder Gangers absolutely hate me, but, c'mon...they don't matter.

" @Mrnitropb: Apparently there is one...

SPOILER WARNING: Click here to reveal hidden content.

Nellis Airforce Base - Hanger - South End on Shelf

 

"

" I'm close to 60 hours in and I've been deliberately avoiding the storyline, just scouring the wasteland and improving my character. I've only found 1 schematic thus far. It's pretty cool how many different ways people play this game. At the moment, I'm just trying to clear all the achievements, and stay in everyone's good reputation graces. Well, the Powder Gangers absolutely hate me, but, c'mon...they don't matter. "

" @INV2 said:

" I'm close to 60 hours in and I've been deliberately avoiding the storyline, just scouring the wasteland and improving my character. I've only found 1 schematic thus far. It's pretty cool how many different ways people play this game. At the moment, I'm just trying to clear all the achievements, and stay in everyone's good reputation graces. Well, the Powder Gangers absolutely hate me, but, c'mon...they don't matter. "

SO true about the powder gangers xD "