You can watch Toy Story an infinite amount of times, and you still might not catch all the gags, references, or even background characters. As it’s been said before, every frame serves it’s purpose, and there sure is a lot going on in every scene. Just list anything that may have gone over the head of the average viewer:
-Woody’s expression changes between shots while Andy is playing with him in the beginning
-While the mutant toys block the door, Jingle Joe can be seen scouting the outside in the background (probably for Scud)
-After the mutant toys celebrate their victory, the Pteridactyl accidently knocks over the solider with no arms, who has trouble getting back up
-After Andy’s toys are celebrating throwing Woody off the truck, Bo is consoling Slinky by patting him on the head
-Mr. Potato Head is singing karaoke for ‘We Wish You A Marry Christmas’ on Mr. Mike, with the lyrics by Mr. Spell
-This one’s more of an Easter egg; Zurg can be seen in one of the pictures Andy drew of Buzz. I originally thought it was just his shadowy figure, but I guess the original design had him all black
I saw some of the ones you listed. I didn’t notice a few of them. But, I agree no matter how many times you watch it, you always notice something new.
There are so many things like this, and even little mistakes that I never noticed until I started the Live-Action Toy Story Project. Look that up if you don’t know about it yet. We try to match everything as close as possible, but that’s when you notice those things, watching a frame at a time.
Must require some patience! It’s a wonder how they were able to cram so much into a single frame, yet not make it seem crowded. Of course, I think I do know what you’re talking about when it comes to mistakes. I think some of the moving van scenes, which had Buzz and Scud microscopically in the backgroad, had them out of sequence.
I agree. You never know what little qualities you can find in a film.
It wasn’t until the second time I watched Toy Story 3 when I heard Mr. Potato Head yell “And I would’ve gotten away with it, too, if it weren’t for you meddling toys!” 
And for whatever reason, I didn’t notice the hilarious face Mr. Potato Head makes in Toy Story 2 after trying to unlock the car until about a year ago.
I also noticed a bunch of stuff when I saw Cars 2 for the second time on Labor Day weekend (they re-opened it just for the weekend). Like [spoil]one of the sponsors being John Lassetire at the World Grand Prix, The Incredimobiles showing at the Radiator Springs Drive-In Theator, Gastow’s in Paris, A113 in a few places, the Wilhelm scream,[/spoil] etc.
[spoil]I thought that both the John Lassetire sponsor and Gastow’s were really funny and great references.[/spoil] I love the Potato Head line from Toy Story 3 that you mentioned.
I thought that the line that Potato Head said was pretty funny. Also, there were some pretty cool references in Cars 2 that I saw like the Brave one.
Huh… I must not be very observent, cuz I have not seen any of that in the movie, I’d better watch the movie again and this time I will look harder! 
With most, it’s not vital that you see them, they’re just added details (though some carry plot relevance). I found it strange how the mutant toys blocked off the door (they had no means to communicate), but it became clear that they were trying to warn them of Scud.