We have experienced the same problem as well, especially with out Fall Carnival. It needs about 60 people to run it successfully without stress. In past years we have only managed to get about 20 parents and had to depend on high school students (football team, cheerleaders, Key Club, etc.) to help out with the rest.
This year, as an incentive, instead of offering a drawing for items we are offering a "homework pass" for the carnival. It is fully supported by our Principal so it will work with any teacher in the school. It does have a few limits to it (can't be used for projects or test prep, etc.) Any parent that volunteers at least one hour, the day of the carnival, will get a one subject per student in their household homework pass (only one per student per family allowed) that expires at the end of the first semester. We are just now starting the volunteer drive for the carnival... so only time will tell if it works or not but so far the initial feedback has been great!
To help entice teachers we are basically doing the same thing only it is a 1 hour pass for "copy help, lunch duty, project help, etc."
I agree that we shouldn't have to "entice" parents to volunteer, especially for events that CLEARLY help their children and school. (We do the carnival instead of fall catalog sales at the request of the parents!) But... when we are competing with football, dance, cheer leading, soccer, scouts, etc. etc. etc. something has to give.
This is something that doesn't cost us anything, parents (especially the super busy ones) will want/appreciate, and it gives the kids an incentive to "help" encourage their parents to participate/volunteer. Kids are the best marketing tool we have after all... excite them and the family follows!
(This idea actually came about from a
pass
we found in the File Exchange! We just created our own and made it to fit our school.)