I agree with Jeff, PP Nachos and sandwiches go really well for us. We do both pulled pork and pulled beef (chuck roasts) - and have a pretty good response from those items. Ribs are a mess to vend IMHO - to make enough money to make them worth the time they will end up being expensive - and the public 'generally' doesn't want to pay what I need them to to make ribs worth my time.
I like festivals (since I don't have a friend with a gas station...lol) - but I watch the entry fees closely and have learned that most of the organizers' numbers are off as far as guests....it's usually much lower - so I make sure I cut back on cooking so I can hti the sweet spot - we recently sold out all 3 days at my last festival, so I'm getting better at gauging attendance and how much to cook.
I've made as much as $4000 over a couple of days, but luckily have always broke even or better at all the events I've vended. I do catering as well - and much like Jeff, the price is what it is. I've found if they want it, they want it - no questions asked. It is much easier than vending however for sure (at least IMHO)
For cpw - a haystack is this - per jbrink01's post -
"We do something very similar called a Haystack. Build in this order; Fritos, PP, Sauce, Shredded Cheese, Shredded Lettuce, Diced Red Onions, Ranch Dressing."