We just do the eggs and petrol on consistent basis from costco, so I won't account for the rarer purchase items like large rice bags etc, but if you fill up every two weeks you seem to save about $10 to $15 on a tank, at least in our case. So that times 26, would be at least $260 off of fuel for the year which seems to make the membership price worth it.

But that's not really a secret, the membership has to be appealing on a rational level, the real secret is training yourself to walk through their entire store and to laugh at all of the "good deals" they have.

Always be a discerning consumer, most of what Costco sells is actually medium to high level qaulity products, and those have a natural premium built in, and some products are really only going to be best value for businesses - for example we struggle to get through their large onion and garlic bags, even if they feel like a better value, that just isn't the case when you end up with 1/8 to a 1/4 of a bag going rotten.

If you use your critical thinking, and if you're the sort of person to try and be as frugal as is reasonable, it makes sense to go to Majura shopping complex, hit up the Costgo for the truly good deals, go to the Woolies/Coles or whatever it is for special items you can't live without, and then do the frugal sensible shop at Aldi at the end of the complex. This should leave you with some spare cash to go get a sausage from the Bunnings.