We have a commercial type popcorn machine with a 12oz kettle (great northern from Amazon). We purchase the proportioned popcorn from gold medal. It is a HUGE hit and we always get compliments on it.
Depending on when sunset is, we will either incorporate dinner in to the potluck concession stand (aka 2 6' folding tables) or keep it a potluck dessert concession table. Whichever the case, we ask the guests to bring something for the table and a 2 liter. We supply the plates, plastic utensils, napkins, cups and ice.
Our pre show entertainment has been trivia recently. There is normally a 10 minute break before the movie starts; this is when we start popping the popcorn. We don't have a warmer for bagged popcorn, so my wife scoops and bags the popcorn for each person.
I recently found some coated popcorn bags on Amazon. 1oz size I believe. I haven't had a chance to use them yet. But will be perfect for the butter-like topping I have.
I'm considering selling movie theater candy as a way to offset the cost of maintenance and upgrades. I haven't convinced myself that it'd be a success with the potluck concession table.
I don't feel like I gave you a proper answer to your question. about selling candy. This is what we sell and what it costs.
Prices at the snack bar:
Popcorn $2.25 Small - $3.75 large
Cheese Pizza $10.99
Peperoni Pizza $11.99
Beverages : Cola, Diet cola, Root Beer and DP. $2.00 a can.
Of course you can see it's all over priced, but it's a suggested donation. We have someone, typically it's a volunteers, sit at the table. The prices are on the table in front of the popcorn and the soda. Then there is the pizza sheet taped to the table. The primary reason for someone monitoring the table is to keep bags of popcorn in the warmer and cook pizza when it is ordered. Also to say hi and welcome folks in ect. Then at the end of the table is a container that the guests put money into. The prices are a suggested donation and guests are welcome to bring in any food / drink they want. We just ask that if we have it you buy it from us to help support maintenance of the theatre.
Sure there are a few folks that bring there own popcorn in anyway and never "buy" ours. But then there is also the guy that comes in almost every Saturday night and drops $10 in the can each time without taking anything, so it balances out.
Personally I'd try it. Make sure your guests know what your doing and why your doing it. I think if it was me I'd ask folks not to bring whatever types of candy your going to sell and set up a special area on the table for the candy. with a sign indicating the prices and that any money made off of the candy goes towards potluck supplies and other theater equipment maintenance and a jar for folks to put their money into. The worst thing that will happen is it'll sell slowly. I just don't see how it could go wrong really.
Also I would like to suggest you at least consider selling your popcorn or giving it away for a suggested donation. It's your machine, it's all your equipment and supplies and I doubt that anyone is bringing in popcorn now, since your popping it fresh. You wouldn't be competing with the potluck table that way.
Those are my thoughts anyway.