I am a great hater of the overuse of plastic, and either try to re-use it as far as possible to avoid excessive consumption, or cut out its use totally. Maybe we could turn this into a thread where people add thier tips here.
Here are my most common things that I do.
Food - like yoghurt or margerine - containers get used until they fall apart for starting seedlings off in the greenhouse
I use washable cotton bags when I go to the shop, instead of using the shops disposable plastic carrier bags - and the oldest of my cotton bags - well its still doing strong since I got it in 2004!!!!!!!!!!!!!
I cut plastic beads off old clothes or broken costume jewelry and either re-use them or give them to someone who can.