So, I only bought the car so I had a place to store things. I don't want to deal with having to replace the Microfusion Cells and having to go back to get the car if I leave it somewhere to do a caravan mission. So I'm going to leave it at Redding, I may use it later (I know it goes a million miles an hour) but I want to save my MF cells for energy weapons. My question is, will people steal things from my car if I leave it there? I have a bunch of stuff in the trunk that is worth a lot of money in total.

No, nobody will steal your items. Just don't park your car in New Reno (Virgin Street), or you'll have a surprise.

Pshaw!

Parking my car in New Reno is the first thing I do when I arrive! It provides excellent opportunities regardless of your character's inclinations or play style. Besides, even during all of those shenanigans your trunk is still freely accessible.

Yes, because you already played the game, so you know how to benefit from the situation.