There are a lot of questions from new Amazon FBA booksellers about which supplies to use, what do you really need, etc. Here is the list of items and services I currently use and deem essential to find, clean, and ship my books and other items. I run my business lean [which means: I am a frugal Pennsylvania Dutch person who prefers to spend as little as possible 
] but I can’t do without these items. These links are to purchase on Amazon – if you click on the links and buy them, I get a few pennies to put toward hosting.
Scouting for Books to Sell
iPhone or other smartphone (I use an iPhone 5)
Neatoscan/Scoutify app ($40/month)
Unitech handheld barcode scanner (~$200, one-time purchase)
Anker portable USB Battery backup ($30)
These items allow me to scan books, media, and grocery products, even when I do not have Internet access (in a library basement or something). I find the handheld scanner effective, long-lasting, and less bulky than a socket scanner so many booksellers use, plus it allowed me to just use the smartphone I already had.
Cleaning/Prep to Sell Books
USB barcode scanner that works with an Iphone or smartphone
Scotty peelers to remove labels
Impulse sealer (I like the 16″ one because it’s big enough for large polybags)
Old clean t-shirts for wiping down books
Polybags (this is a nice assortment of sizes to get started, plus they are self-seal and have the suffocation warning on the bag, making your life easier)
Shipping
Amazon FNSKU Labels (I’ve found the generics to work just fine but you can also use the name brand Avery ones)
Cardboard boxes (usually I order from Uline or Home Depot)
Packing paper for dunnage (I also just reuse air pillows from personal Amazon orders)
Shipping tape (I’ve been using this brand for a year. It works great even though the brand isn’t well known.)
Business Management
YNAB
Google Maps
Excel for mileage tracking