a few Ideas that have wroked in the past
If you don't have any budget get people to donate as much as possible possibly hold a raffle too, always helps...
Some Local Radio, Newspapers, Websites or TV stations especially will do free advert. for charities...
Someone directing traffic/parking...
some well placed traffic cones & yellow caution tape if needed
Someone taking donations/entries & have a secured area with a lockbox/cashbox etc.
Plenty of water & ice at-least or something cold to drink
{especially in the summer}
trophies &/or plaques for winners of classes, maybe get a few local shops to donate some stuff, cleaning products & freebies/grab-bags for show entries or even larger donations, also helps to get donations from local businesses..
food/souvenirs
{T-shirts or Hats, try to find someone to help or donate, Car Dealerships are a good place to try to get donations}
or some form of concessions, will always make money, especially if it's for charity
{donate the proceeds/profits to the charity}
sound system & some mellow music is always good
{not something obnoxious, no Rap or Head Banger stuff, a good variety, top 40 stuff/golden oldies, works well},
Use or day-event permits if necessary, tax forms for charity funds {some towns require it},
your church may have the rights/forms necessary already
insurance/liability, if it's needed or the church doesn't have coverage already, a must
{some unscrupulous people are suet happy}
& porta-potties & garbage cans are a must have too,
try to get some church volunteers to help with traffic, parking, music, concessions, sales, give-aways, clean up & judging etc.
It's been a long time since I did one & it takes some "good & dependable help" to pull it off...
Good Luck