Thoughts:

If you ask a local pub landlord or the venue to provide a bar, make sure you discuss beer prices beforehand to avoid profiteering. You also need to explain about folkies, or they'll provide lots of lager and no decent ale.

Don't sell food separately - lay something on and include in the ticket price. You should find a local cafe or sandwich bar that can provide a cold buffet for you to collect on the day for a reasonable price. I'm sure all the organisers will donate raffle prizes - but not too many!

Budget on selling half your tickets when you do the costing - and just in case, decide how much you are prepared to pay to cover a shortfall. The band will want payment, even if nobody turns up.

If you've never run one of these before, agree a cut-off cancellation date and a cancellation fee with the band.

Create flyers and leave them everywhere you go (to access like-minded people); the band members are often a good source of free publicity too, and can leave flyers at their other gigs.

Check the acoustics of the venue and power supply availability before you talk to the band.

Finally, if it's raising money for a good cause, people may pay a little extra for tickets, but under no circumstances expect people to give an agreed service for a reduced fee. One organiser tried to fob me off with a reduction in payment on the night because it was a charity do. When he gets out of hospital..... However, we do often return a portion of the fee, once paid, as a donation if it's a good cause.

Good luck, have fun.