Raising money with a barbeque
Hold a barbeque for friends and family. Or invite neighbours, work colleagues, school friends etc as appropriate. You can get them to buy a ticket or ask for a donation at the event.
You could make it a bit more of a public event by advertising locally and selling tickets or making a charge for people to attend.
If it is a public event you may have to get permission from various authorities. Check before you start spending money or booking halls etc. The local council could be a good starting point.
Events organised in school grounds or village halls etc will probably be easier to organise because someone will have done what you want to do already!
IF you want alcohol to be available then you must make sure that you get the appropriate permissions and licences.
The main point is to have a fun day