This is what I do to skip the lines at the post office. I just drop off my books at any USPS collection box (blue mailbox).

Note: I know that you can get an online account at paypal or Endicia or USPS.com or wherever.  This is an "offline" solution for people like me who don't like having too many online logins.

(1) I use a digital kitchen scale that I got from Walmart. It can measure up to a tenth of an ounce. It is cheaper than a postage meter but still as good. It is important to get the digital kind because the analog ones are not very accurate. I have been using my digital kitchen scale for three years now and it still works great.

(2) I buy stamps from the USPS Self-Service Kiosk (formerly known as APC, Automated Postal Center). It is like a vending machine with a touchscreen. I pay with my credit card. I select "buy stamps" and when it asks me what value of stamp, I select "other", and enter $2.80. You DO NOT NEED a destination address to buy these stamps, so you can buy a bunch of them in advance.  I buy a batch of 10 stamps, and use them one at a time when I get a book request. 10 stamps at $2.80 each comes out to $28.00.  The stamps look like this: http://i.imgur.com/iszkIdi.jpg   These stamps allow you to skip the post office counter, even if your book is over 13 ounces!!!  If a heavy book needs more than $2.80, I just add forever stamps to bring it up to the correct value.  For example if the book is over one pound, $2.80 plus a regular 55-cent forever stamp brings you to $3.35.

https://faq.usps.com/s/article/Self-Service-Kiosks

(3) For tracking, I use the USPS tracking label #400. These are available for FREE from the post office counter. The last time I asked for them, the kind lady gave me a whole roll of these labels! You have to be clear what you are asking for, because some new employees might not know what they are. Ask for "USPS Tracking Label 400". It also helps if you show them what it looks like: https://www.usps.com/c360/images/USPSPrePrintTracking.jpg

The label has a top portion with the barcode, that you stick on your book package. You keep the thin bottom part with the tracking number -- stick it in a notebook for safekeeping. Wait about 24 hours after mailing your book, then you can look up the tracking number on the USPS tracking website.  https://tools.usps.com/go/TrackConfirmAction_input

Another way, if you have a PayPal account, is to go to 

https://www.paypal.com/ShipNow (you can use PayPal's corporate discount, and you don't have to go to the PO even if over 13oz)

Courtesy of my favorite postal website, which lists all USPS prices in an easy, digestible reference format, with wry asides:

https://www.nerdylorrin.net/jerry/postages/

Update almost 2 years later:

I'm still doing the things I detailed in this post.  The USPS self-service kiosk no longer lets me choose a custom amount for stamps, but I choose one of their pre-set amounts, somewhere in the 2-dollar range, and make up the rest with regular postage stamps. The last batch of stamps I got from the kiosk were $1.96, so I need to add two forever stamps and a ten-cent stamp.  1.96 + 0.58 + 0.58 + 0.10 = $3.22.  I confirmed with an employee at my local post office that I can still drop off books this way.

Someone on PBS told me about Pirate Ship. You can do both USPS and UPS with no additional charge, in fact you can get the good rates that PayPal offers. And then you can have your books picked up from your box or drop them off at a blue box. I have been using it for a couple of years and probably won't go back to the post office except for stamps and special first class mail. Check it out: https://ship.pirateship.com/ship

I love Pirate Ship, Judith! I've been a "pirate" for over a year now, and it's the simplest way to stamp up and ship out. I never have issues with the website, it's easy to reload, and I use it for all my USPS/UPS shipping needs. It's rare that I have to go inside an actual post office anymore. Next, I'd love to get a thermal label printer; I know many of them integrate with Pirate Ship. I recommend PS to anyone looking for a way to skip the PO lines.

Also, they offer discounted rates on standard postage (not media mail), which is a huge plus.In fact, at Christmas I wanted to ship a large package to GA via UPS. At the counter I was quoted over $100 (as if). I went home, boxed it myself, and paid only $35 via Pirate Ship. Yep, I'm very happy indeed.

huge fan of pirate ship also!! user for 3 years now and the only time I go to the PO is to get our snail mail and drop off mail inside after hours, twice a week. Haven't been to the 'counter' in over 2yrs since I also order stamps online when needed. It's a huge discount for my mailing/shipping budget. Last package I shipped saved me over 32% verses the counter price. Won't be needing the 'counter' anytime in the future. 

Another Pirate Ship fan here, thanks to Nancy D. mentioning it.  It's so easy to use!  I do use it for PBS books, but I've also saved money shipping out other packages.  Absolutely love it!

Ok, if I am trying to save $$ on large or heavy Christmas boxes I am mailing 1000 miles .......Pirate Ship shows discounts on UPS and PO delivery......so that means I would buy postage using Pirate Ship membership and print a label showing I paid then take packages to either the UPS store or PO  near me depending on which service I chose?

That is correct, Jeanne.  Once you've purchased your postage, you print your label and tape it on, then just drop the box at the PO or UPS, depending on which service you chose.