I really have little idea of what happens in all other areas of the country, but I think here you definitely need another job if you can't take off at a min. several quarter to half days a year (3-4) for your child's school in this area. There is just no way around it IMO. I would even say the best thing would be able to take off for several hours once a month for various activities if you really want to have some hand in the school community and your child's education. Plus I find I have to take off for other enrichment activities, but maybe that's just me. Most working moms I talk to say flexibility in a job is the most important thing in balancing parenting and work. Other important aspects that moms consider are more vacation/less hours, less facetime required, less travel, and good maternity benefits. If your job doesn't have any of these things, I think it will be very hard to juggle everything.
And I know several areas where parents are expected to monitor recess and lunch in public schools in addition to library and art, so being available only for open house, conferences, and an activity like the thanksgiving lunch is hardly much involvement required compared to some areas of the country.