Buy the specially marked Dorito's or Mountain Dew's that have codes on the back of them. Then redeem the codes on dewxp.com for the USA, or on dewxpcanada.ca for Canada.
I don't eat that crap. I have like 1 pop (soda) a week. I just gave it to my friend, and he split the cost of everything with me so I get the codes, and he gets the food.
If Halo 4 is as good as Halo 3 and Halo 2 it could be one of the best games ever. I hated Reach, Wars, etc. The "Custom Games" with 'Fat Kid' on Halo 3 were probably the only fun on Xbox in a long time.