I prefer add-on items instead of the alternative with Prime, which is to charge more than I'd pay at the local store because of shipping charges for a little item under $10. You're not going to find a great price on something that costs $6, but costs Amazon $3 to ship. I've passed on buying probably hundreds of small items using Prime because they cost more than at the local Walmart, Lowes, Home Depot, Target, etc.
I always keep several dozen items in the 'Saved for later' part of my shopping cart. If I want to buy a $3 add-on item, I just buy that extension cord, frying pan, memory card, sheet set or book that I was going to buy anyway.