There's been discussion on other threads about some "thrifty tips" which don't seem all that sensible, like rinsing the sauce off spaghetti hoops to reuse the cooked pasta (wastes sauce and calories), or boiling soap to make shower gel (wastes electricity and soap - better just use the soap bar). What other thrifty tips have you either invented or tried, that you would warn other people off?
Here's mine: people have said a pinch of cheap curry powder helps elevate all kinds of dishes, including baked beans, tinned tomatoes, etc, and helps ring the changes in a monotonous diet. Here's what curry powder doesn't elevate, kids: porridge oats. Many, many years ago (pre DS), desperate for something other than plain porridge made with water, which had formed the bulk of our diet all week, we tried currying the porridge with an onion. Now, if I make or buy terrible food, I'll still usually eat it anyway, and just determine not to buy or cook it again. Not so this: oats, curry power and the onion all wasted. Don't ever repeat my mistake!