Stores are getting trickier and asking for different parts of the packaging now. You will need some boxes, and it will take some room, but file these things away in an orderly fashion. Put them in your garage or somewhere that isn't a fire hazard. Keep your receipts also, as you will need them for the rebates. Always check out the boxes for special offers.
Many cereals offer little toys or other things that can be used for birthday parties or small gifts.
It may be worth sending off for them. It's a lot of work, but if you are organized and skillful, you can save a lot of money on food with coupons and rebates.