If you've ever been to a Sam's Club (and I was a member a few years back), then the experience at a BJ's will be the same. Gigantic big box store (larger than your typical Wal-Mart) with high bay racks of storage that go all the way up to the ceiling.
BJ's is a membership store and while you can do a trial shop (15% surcharge), you're better off simply joining for $50 a year. Yes, the do have specials and discounts but those are not year round.
As for the stuff, well, there's nearly everything. You might not be able to do a full grocery shop but you can certainly buy up a cartloads worth of stuff and in the process save some money on the bulk. Two-packs of some things seemed to be maybe half-again the price of buying one at Harris Teeter. Others are competitive with what you might find at Wal-Mart.
I was impressed with the decent selection of pet food products, including a 50 pound bag of the same dog food I usually get at Petsmart but $10 cheaper.
So yes, I joined. And I'll be back.
The gas is cheaper than others nearby but it's still more expensive than going to South Carolina.