My mom taught me to open envelopes horizontally with a letter opener. After you take out the mail, you can use the back of the empty envelope to write your grocery list. You can even put coupons into the envelope. This also works for errands.
I post the envelope on the fridge next to an IKEA pencil I've attached to a magnet with thread.
With eco-conscious living being "in" right now, I can tell people that I'm being "green", not just dorky.