From my experience, it’s easy to pick Amazon as the first source for whatever you might need, but I’m finding that certain things are usually cheaper from other places. Here are some examples…
Name brand toys: Amazon is the go to, but Target and Walmart often have the same toy priced for less.
Random toys: With non-name branded toys, ebay is my pick. Toys like fidget spinners, marble tracks, etc. Virtually infinite number of sellers. Just be sure to check shipping, reviews, and the shipping estimate. Some items ship from Asia, and it can take months to arrive.
Specialized batteries and miscellaneous cables: Same with random toys, ebay often has many specialized batteries (not AA, AAA, A), but rechargeables, 18650s, Lithium, CR2032s, and cables at much less. The complaint about ebay is that it’s difficult to trust a seller and there can be overwhelming number of choices. Also, since you don’t know who’s the seller, you might end up with batteries that are close to expiration or even counterfeits.
Household items: Nothing really beats Costco and Sam’s Club for most household items even if Amazon puts out a really good deal. Household items like laundry detergent, trash bags, baby products (diapers, wipes, and formula) and Ziploc bags. Unless you need to fill up your Subscribe & Save, I’d just go down to your local warehouse club. Also worth noting that Costco accepts coupons for baby formula (Enfamil is an example and they send out coupon checks for $5 or more). I think it’s the only coupon Costco takes.
That’s it for now. Don’t forget to use a site like slickdeals.net to do a quick search for any items before actually buying it. You might find a good deal and/or get an idea of what is the best prices you might find for your item.