I can't speak for Costco, but I have experience with Sam's and BJs (the store darn it, not "that's what she said!" Lol).
I find that both don't actually offer deals, maybe slightly over a retail store, but not if you shop online or are a smart shopper. Both offered bulk, but the limited selection means there is often only a brand, maybe two. Usually I find what I need cheaper at WalMart or Kroger's. Travel packages are easy enough to find online, same with the other things you asked of.
No judgement! But I find those clubs are just for people who don't want to shop with the rest of us normies. I have a Sam's card now, because it pays for itself when I do the Groupon/whatever deal and the free stuff one gets. I only buy a specific snack there. They only have one flavor, but their price is 25¢ or so per bar less.
If you want to take the easy way for an okay deal (no judgement! You do you
), then go for it. Otherwise I'd say really check the exact pricing and see if it really is a deal. At least for Sam's, now, it isn't.