Picnics have been okay in the parking lot in past years. When I go, we store a cooler in someone's trunk, then just leave and have our sandwiches on a patch of grass in the lot. Nobody has given us any trouble for this. Outside food and drink will definitely not be allowed in the park. Sometimes they say okay to bottled water, but most times not. You get a stamp so that you can leave and re-enter anytime during the day.
For anyone who can't make the weekday, there will be a cosplay picnic at Centre Island on Sat Aug 11th. So you can still get together with a casual cosplay on a Saturday. I'm sad I can't go this year because I have a family thing in Hamilton