On the first day of Rosh Hashanah (if it doesn't fall on Shabbat), the custom of Tashlich is practiced. This involves going to the banks of any river, lake or stream, and literally and symbolically emptying our pockets into the flowing water - an act meant to purify us and wash away our sins.
Many people, in addition to turning out their pockets to shake out lint or crumbs, throw additional breadcrumbs into the water. This custom comes from a verse from the prophet Micah: "And You [God] shall throw their sins into the depths of the sea." (7:19)
This year, maybe you and your family can participate in a Tashlich walk.
And at lunch on Rosh Hashanah, have family members think about how they can make themselves better people. How can you be nicer to other people?
What are one or two things about yourself that you could change? Maybe you could listen more to your parents and teachers, clean up your toys and practice sharing.
Once you have these ideas, gather up a baggie of breadcrumbs, and go together to a nearby lake, stream or river.
As you throw your crumbs into the water, say out loud: "Next year, I will listen more," or "Next year, I will become better at sharing."
Announce whatever it is you have decided to throw away.