So I've been asked about packaging comics for shipping after they're sold on eBay... and I figured I may as well share my tips with all of you!
The first thing to consider is how you're planning on shipping your books. Are you going to ship UPS, or through the Post Office? If through the Post Office, are you shipping Priority Mail or Media Mail?
I don't have any experience shipping comics via UPS, but I have done a lot of shipping through the USPS. Generally, I offer my buyers the choice of Media Mail or Priority Mail. Either way, I always include Delivery Confirmation, which doesn't cost much more, and you can include that in your handling fee.
For sending a single book, or even up to five books, you can use USPS Flat-Rate Priority Mail envelopes, which are free. These are great to use for your Priority Mail customers. You can order other Priority Mail boxes for free as well through the USPS website, and I'd recommend you do so -- especially flat-rate boxes, which can, in some instances (when a lot of books are being shipped) cost less to ship than Media Mail rate! You should also get some of the Priority Mail Tyvek envelopes, too -- they're great for sizes that are too big for the flat-rate envelopes, but too small (or light) to take advantage of the flat-rate boxes.
OK, now for supplies. I can't stress enough that recycling is a great way to go for this kind of stuff. Around our house, whenever we get anything shipped here that comes with bubble wrap, I collect it all (unless it's too small to be of use) and stash it in my office. If you don't get many packages, you may need to buy some... and if you're going to be selling a lot of books, it can be worth your while to go to Office Depot or Office Max and buy a larger package of bubble wrap.
Save all the corrugated cardboard boxes you get, too... even if they're not the right size, you can still use them -- you can cut pieces that are about 1/2 an inch wider and taller than a comic book, and put books between these before putting them in an envelope (you can use the bubble wrap around the books before putting the cardboard around them). You can often find cardboard boxes in recycling bins, too -- and comic book shops always have boxes every week from their new shipments that you should be able to get (some of these will be the perfect size for comics, too!).
Save any packing peanuts you get, too... they're a good, lightweight way to fill in spaces in a box and prevent stuff from moving around. If you check with some smaller stores in your area, you may even find some of them always have to throw out their packing peanuts because they don't ship anything out (in Tacoma, there was a costume shop that called me when they had a garbage bag full of packing peanuts so I could pick them up).
If you can't get packing peanuts, ask your local newspaper if you can get the rolls of leftover paper from their press runs. They're usually happy to give these away to anyone who asks for them... wadding up some of this can fill in empty space in a box without adding to the weight.
Some stuff you'll have to shop for are envelopes. Padded envelopes are nice to have (and eliminate the need for bubble wrap). Good places to buy these are your local dollar stores, where I've found 8.5 x 11 two-packs for a buck, as well as any liquidation store (I don't recall ever seeing them at Big Lots, but I have bought them at other non-chain liquidation stores). If you buy them by the case, you can usually cut a great deal (when I was selling records, I found the perfect size at a liquidation store, and they were about half a buck each by the case).
Manilla envelopes also work, too -- if you're shipping a single book media mail, placing it between two pieces of corrugated cardboard and then into a manilla envelope will be plenty of protection. I've found these at Big Lots, and other liquidation stores are good for those, too.
Another Dollar Store item you can find is the brown paper used for wrapping packages. When I've had to cut a box down to a custom size, I'll often wrap it in the paper -- this eliminates the need for covering up any markings on the boxes (a requirement for shipping). I've even done this for smaller packages where I just had a few books bubble wrapped together, then cardboard on either side, then wrapped in the packaging paper.
You can find packaging tape at the Dollar Stores sometimes, too, but it's more cost-effective to get it at an office store... buy a multi-pack of fillers that come with a reusable dispenser.
I'd also recommend getting some label paper, too, so you can print out your address labels on the computer and peel the backing off to put on your packages. This just looks better, and you can easily add a reference number to the label (with, say, the item number from the auction).
The only other piece of equipment I can recommend getting is some kind of scale. Don't feel you have to buy a postal scale -- they're pretty expensive! It's much more cost-effective to buy a food scale! After all, you just need to know how much it weighs to the nearest pound without going over it! Any package that's going to be too heavy for a food scale (mine goes to 10 lbs) can go on your bathrooom scale.
Whenever you do your packaging, always bear in mind that you don't want any adhesive to contact the comics themselves. Having the books in bags will help eliminate this from happening. If you anticipate selling multiple books to a single bidder, buy some magazine-size comics bags, and you can fit a fair amount of books in one of them. If your books are all bagged or slabbed anyway, you won't have anything to worry about!
Always make sure your packaging is secure... there shouldn't be any place on the package that could get caught on a corner and torn open. Don't go overboard on the tape -- just make sure you use it wisely.
I always recommend figuring out your shipping costs before listing your items -- don't make people ask! And offering that choice between Priority Mail and Media Mail buys you some goodwill, too.
Oh, when you prepare your mailing labels, I recommend putting on the bottom of the label how it's going to be shipped (this saves time at the post office). If you're using Delivery Confirmation or other confirmation, have a stash of the forms at home, and fill them out and put them on the package before you leave. If you're going to have a package insured, I usually put the code "I" with a number after it on the label, so I know how much it'll be insured for. The more organized you are at the post office, the faster it'll go, and the less dirty looks you'll get from people waiting in line for you to finish!!
Any questions you might have on any of this, please let me know, and I'll be happy to amplify or explain anything in more detail!