^I'm not sure why they didn't carry over/expand FO3's junk weapons to New Vegas. Those were always fun to build and gave a use to some of the more useless junk (toy cars, motorcycle handbrakes, etc.) They reintroduced the Shishkebob in Honest Hearts, but there was no way to build it from scratch.
Speaking of trash, there's one place in NV I always feel COMPELLED to clean up whenever I see it. The office suite with all the junkies in the Aerotech Office Park has a gajillion tin cans lying around on the floor, and I always gotta pick them all up and dump them in one of the trashcans.

I've also in the past picked up every single object in the Sierra Madre and deposited the useless items in a trashcan by the fountain as well.