This almost sounds depressing, but in general Katy and I probably get 400-500 of our membership fee back. This is a combination of having an executive (2% back) membership and having the costco amex (1-3% back depending). The amex we solely use for gas (mostly from costco since it is almost always 20cents cheaper a gallon).

We have probably a larger place to live than anyone who does not own their own home, so we can buy in bulk and do so. All told we probably get about 400 dollars cashback a year as well as whatever savings we make from buying bulk.