Bulk shopping is only worth it if you use everything you buy. If you buy 10 lbs of bacon and only use 2 before it goes bad, you're paying too much.
I used too keep a mini fridge in my office stocked with different kinds of cokes. I bought them by the case (24 cans) at Sam's for about 7 bucks. I sold them for 50 cents each which was cheaper than the vending machine.
$5 profit per case adds up quick once word gets around the office. I was buying about 4-5 cases every couple of weeks. That paid for my mini fridge in no time.
So yes, depending on what you buy, Sam's is a great way to save some money. Plus, I believe their gas is a little cheaper.