Packing will help.
As for the play first, eat second issue, you can google this because there is information and articles about the benefits of having recess before eating for younger kids, they actually eat more that way when they are not excited to get outside.
However, I do urge you not to bring this up with either your PTO or PTA, because this is not an issue that they can take on, it is one that you should address with the school administration first, and see if you can get a group of like minded parents together, with your administrators support, to pettition the Board of Ed for this change. In some cases, the change may be totally within your principals control, and having that individual on your side is essential, so play your cards right. It is mostly an issue for the youngest children, and since this involves something called the "master schedule" think next year...but get started now.
It is really not a health issue, per se, but it is a healthy life style issue, as children learn and feel better if they have had a full lunch.
M.