You get to feel good about not buying stuff, and then the next day you still get to buy stuff!

Alright, alright, they do have better ideas for a "delay gratification" message. Credit card cut-up (pre-commitment) and zombie walks (exposure) sound like good ideas.

Don't make a day about not doing something negative, make it about doing something positive. Don't turn off your power for a day, spend a day installing better insulation so you need less power.