The problem with reusing the plastic bags is that they rip out at the belly seams if you carry anything heavy in them. I use them to scoop pre-owned kitty litter into.

I'm surprised that no one mentioned warehouse clubs or coupons. Using both of these can add up to a bundle. I haven't done an in-depth calculation, but I figure I save 5-10%/unit by using coupons for such basics as cat food, kitty litter and TP. I have always looked for the best buy (I'm still a broke grad student at heart.) We buy very little pre-made stuff and mostly do our own cooking, and sometimes the cost per meal is staggeringly low. It's always a tradeoff between time and money.

I'm not looking forward to buying heating oil this winter *shudders*. At least my electrical is from nuclear, and the price has been pretty stable.