Since this is going up over the summer, you could start with some of these:
Summer registration packets
Best deals on school supplies
The PTO's plans for the coming year
What would you [parents] like to see from the PTO this coming year?
Healthy lunch ideas, tips & tricks
Getting the kids ready for school this fall
Reducing backpack strain
Besides being the PTO President, I am the schools web master too. I've added a message board just like this one to our school web site. I have not showed it to the Principal yet or any other parents. I would like to front load it with some conversation topics first. Any ideas? The Principal is pretty conservative so I'm nor sure what her take on the whole thing will be. We are in Southern California if that gives you any cultural reference; or maybe it's just extra info - LOL.