Okay ... here's a REALLY easy one: use 1/2 the amount of toothpaste you normally use (unless you already use very little). Most people use way more than they need to. A pea-sized ball of toothpaste is more than enough. You'll save money, use have the plastic (if you use half as much, the plastic tube will last twice as long) and consume less flouride (which is proving to be rather toxic).
Of course, you can always brush your teeth with baking soda, and you can buy non-plastic toothbrushes (my favourite are foud at: http://environmentaltoothbrush.com.au/). But if you just reduce how much toothpaste you use, it will make a difference.
Last Week's "Small Steps" post: http://sandiratch.blogspot.com/2011/10/52-small-steps-week-13.html