When it comes to popcorn, load me up with everything. If the theater has jalapenos you know I'm throwing them in there. If I have some extra money I'll throw in some peanut M&Ms too. That's just how I do. I especially love the theatres that sell flavor powder. You can buy a little shaker of sour cream and onion, caramel, cheese, or spicy. Isn't that awesome? The thing is, if you're broke the popcorn is expensive enough. That's when you have to go to the condiments.
I've been known to put mustard on my popcorn, so who am I to judge ketchup? The only thing I've noticed with any wet condiment is that it's not the best theater choice. I don't like walking out of the theater with yellow all over my fingers and clothes.