I would join in but for me going 6 days without spending is pretty normal, so going one more day isn't all that hard....
See we go to the store on Monday usually (this week was odd we went to two different stores, one sunday one monday) that means we fill up on gas on Monday...and that is generally it.. I would say once a month we go somewhere costing money on Saturday (this saturday in fact) other than that..sure I' ll join you, make DH go early for groceries then wait an extra day back to my normal..no problem
But in all seriousness the reason we do it all the time is the simple in store =spent money..so we don't. We might run out of milk on Saturday, or Sunday but we generally just wait a day, one day wont kill us..We have learned just how much milk we tend to need, and just how often we have to buy peanut butter or chocolate. other than that I rearely have troubles....except this week. I thought DH was going to skip the store yesterday and go today...he didn't...he went without the list..meaning no craisins...no butter...no english muffins.....not cool..but hey if I can't make it a week without those two things I am not very creative! (is good for the budget to suffer on occassion..)
Having said all that, I think the challenge is a great idea, might help some people think of creative ways to deal with polar bears escaping from zoos!