Carry a zip-lock bag or other container so that when you come upon edible berries you'll be ready to transport them back to your house to share with the rest of the family.
Choose coordinating patterned paper, cardstock, and embellishments, and store them in extra page protectors or large zip-lock bags.
Make your own crumbs by crushing graham crackers inside a heavy zip-lock bag or buy prepared crumbs.
When packing finger foods, use zip-lock baggies or small plastic containers.
You can also use zip-lock style freezer bags.