I'm assuming/hoping that eBay will calculate shipping correctly if a customer purchases all the items ... ???
Assuming you entered the weight for each book in as 1 pound, in this case the eBay calculator will not get it too terribly wrong. It will simply add up all 8 and charge for an 8 pound package - the actual weight will be a pound or 2 less because that 8 pounds includes the weight of a box for all 8 books instead of 1 larger box. Itoosed all 8 in my cart and it was so.
In general it gets much more complicated than that - especially when shipping say 10 oz items FCP. When 2 are bought, the calculator charges shipping for 2 10 oz FCP packages (2 x $3.46 = $6.92), but the limit for online FCP is 16oz. You either ship seperately, or ship Priority Mail at 2 pounds ($6.52-$10.28), and eat the difference or make a few dollars depending on destination. You need to set up specific combined shipping rules to cover these situations and apply them on a per listing basis.
Going to point out a few things and let the others here field the issues:
We talked about using FedEx in the other long thread a while ago, but FedEx for a $5.00 book is not really an appropriate use. You should be offering Priority Mail (PM) and especially thinking about using PM Padded Flat Rate Envelopes ($6.50) if you can ship the item safely in one. PM would get to here on the West coast almost as fast as the $32 FedEx 2 day, and way faster than Smartpost (8days) or Ground (5days) for only 25¢ to 75¢ more, and you get free boxes or envelopes with PM. For destinations closer to you Priority Mail is way cheaper than either any of the FedEx options. FedEx shipping is for heavier items (10+ pounds) or items that incur large dimensional weight hits (big and light).
The Collapsible Shopping bag: FedEx Ground and Express aren't really appropriate there either (nobody is going to pay $47.48 to ship a plastic shopping bag) From your item description it looks like it folds to 11 x 14 x 1 so would easily ship Priority Mail with no dim wt issues, and Priority Mail is a good fast choice here. Parcel Select isn't any cheaper than PM depending on what you are doing with passing discounts on to buyers so could go either way in terms of on bothering to offer it.
The Glucerna Shakes: Had a heck of a time figuring out if that price was for 1 shake or more. The only place the qty is found is in your payment instructions at the bottom of the shipping and payments tab. Many buyers will just pass on it, and it's a way to set yourself up for a SNAD problem.
You need to put that in the title, in the Item Specifics (IS), and in the body to make it obvious. Use all 80 characters of the title to get as much info across in the search results.
Having said that, your price looks to be high (about double market rate?) And you have it as 10 oz bottles not 8 oz (photo and appears 8oz is the only size sold).
You have both Parcel Select and Retail Ground on there - they are the same service just different pricing. Pick one or the other.
Second category. I don't do it and can't comment on cost effectiveness, but can say I almost never look for anything on ebay by category unless I'm browsing something specific like tennis racquets ending soonest just to poke around. If I were looking for glucerna I'd search it out and category would be irrelevant since there should be few enough returned results that wouldn't need to filter by category.
Try to make Priority Mail work more - especially for the items you have up now. Buyers like it, it's less hassle for you (dump it in a blue box instead of going to FedEx, free boxes, etc), and it beats out FedEx often except for big and/or heavy.
Good luck.
