Even if you have managed to banish the "gimmes" from your home, it doesn't mean gratitude will automatically flood into your child. In some ways I think developing a constant "attitude of gratitude" is a lifelong process. Partially because it takes some life experiences to reinforce how much you really do have to be grateful for in your life. Or perhaps we just become too distracted with the annoyances of life to remember all of the things that are going "right". Whatever the cause, parents can begin laying the groundwork for their children to become grateful.
Perhaps the easiest way to begin with very young children is to insist they use the words "please" and "thank you" consistently. Those were actually some of my daughter's first words (after "Hi!" and "Dada" of course!). Part of gratitude is getting in the habit of thanking everyone for everything. I think there must be something about saying the word frequently. Said often enough, it does eventually seep into your consciousness. Something in your brain clicks as you complain about something minor after thanking five people for their help and thoughtfulness.