Gas cards came!

Remember my post awhile back about the Kellogg's cereal $5 gas card? Well, they came today! 4 of them. You are allowed 5 per family so I sent the 4 in separately(this was part of the fine print) and in a 5th envelope I wrote for a no purchase necessary entry. Today I received a whole empty cereal box, with a sorry try again and another form to fill out for a $5 gift card.
So, in total, I bought 4 boxes of cereal at $4 each. I bought 5 stamps and will need one more for today's form.
I got $20 worth of gas cards, with $5 more to come!
It was fun for me to see that this actually worked as I have never tried it before.
I have activated all the cards and now comes the tricky part, redeeming them! I am told it's best to take it in at any gas station and leave it with them(I am going to bring all the rules to redeem Kellogg's sent me with my cards). Then you can get $5 worth of gas and go in and pay and start again, or you can leave them 2 methods of payment and fill up. I am told this is very hard for them to figure out and it's easiest if you do your $5 transactions separately.
Anyone else try this? Anyone win the $500???