1. What's your favorite weapon in a movie?
You're asking a pacifist here, but imma say Mace Windu's lightsaber, and the reason is the obvious one: the purple "blade"! Samuel Jackson apparently asked for that so his weapon would stand out from the others, and it was a good call.
2. What's your favorite car in a movie?
The first one to come to mind as I read the question was the time-traveling DeLorean in Back to the Future -- between the "wings" (the movie's DeLorean was the first I'd ever seen) and the time travel, it made an impression.
Herbie the Love Bug is my other fav -- my dad's career was spent working either directly for Volkswagen or for VW dealerships, so our family has always had a soft spot for the Beetle.
3. What's your favorite cat or dog in a movie?
I don't tend to watch films with animal protagonists (okay, except for animated films), so I'm trying to think of my favorite movie pet. And ... I guess it's a tie.
Chronologically first is Asta, the Wire Fox terrier played by "Skippy" in one of my all-time favorite flicks, The Thin Man (& three of its sequels, after which "Asta, Jr." inherited the part). The popularity of the character & its portrayer infamously led to a run on the breed, which wasn't a good thing, but you can see the appeal. I read that William Powell wanted to buy Skipppy/Asta, but the animal was not for sale.
More recently, there's that faithful Jack Russell terrier played by "Uggie" in The Artist. The internet says the character's name was "Jack," but even though I paid to see the film five times the year it came out, I'd forgotten that detail. Anyhow, he was a very good friend to titular "artist" George! There was, I believe, a campaign to get the animal an Oscar nom, but it came to naught (though he did win the "Palm Dog" at Cannes).
4. Who's your favorite sidekick in a movie?
Hands down, it's Irving Radovich in Roman Holiday. He's the photographer (played in an Oscar-nominated turn by a youngish, bearded Eddie Albert) who follows Gregory Peck and Audrey Hepburn around town shooting pictures for a story that will never be written ... and he has the memorable line, "It's always open season on princesses." In my RH fan fiction (which you will never, ever read), he ends up with the princess.
(Okay, that "open season" line doesn't play very well post-Diana, does it? Still, no less love for the character.)
5. What's your favorite painting or sculpture in a movie?
I am interpreting this to refer to artworks produced expressly for the films they're featured in. And I'm not sure I have a favorite, so much as a "most memorable." In the 1945 film adaptation of The Picture of Dorian Gray, the title object is the only thing to be shot in color. Painted by Ivan Albright just for the movie, the picture now resides at the Art Institute of Chicago, where I'm sure it is spooking visitors the way it spooked me when I first saw the film on TV some decades ago. I've never seen the movie since, but I never forgot the portrait.