Just a few ideas:
Take your own bags to the grocery store.
Walk to the grocery store.
Switch to energy saving light bulbs.
Take the bus to work.
Plant a salad garden.
Try a meat-free meal this week (then next week, then twice a week, then three times a week).
Choose independent over big-box-chain store.
Buy in bulk to reduce packaging.
Open those curtains and turn off those lights.
Don't buy anything today.
I could go on. The point - take a step to make a change.