Unsubscribe from mail-order catalogs. These things waste paper and pack the landfills, AND they feed the desire to purchase more stuff. You can go to catalogchoice.org to take yourself off the mailing lists. Your postman (or woman) will thank you!
Forget flash sales, Groupon, LivingSocial, etc. The fact that these deals are expiring soon just makes you feel pressured to buy them, and you WILL end up spending money on things that you didn't even know you needed (electric quesadilla maker, anyone?) or that you probably wouldn't have bought otherwise. It's a classic example of a great deal that would save you even more money if you had never seen it.