In my experience sometimes it does help to include the reasons why you are leaving, that way you are not burning your bridges and the superiors know that you were happy but circumstances prevented you from staying:
To Whom it May Concern:
It is with great regret that I must turn in my two weeks notice at this time. Due to rising fuel costs it is no longer financially feasible for me to remain with your company. While I have enjoyed my time here I have to ensure that my family is taken care of financially and my financial obligations are met. Perhaps in the future if the fuel costs and economy stabilize I would be able to return to this company. Thank you very much for the years I have enjoyed with you and I appreciate your understanding.
With Regards,
Insert Your Name
This way you have stated your reasons and they might give you the raise to be able to keep you, you are letting them know you are not leaving due to bad or hard feelings and you are leaving the door open for a return if possible.