Lizzie, internet service, in my case my cable modem, is indeed deductable.
I have not claimed magazines myself because I don't really take any, but I would think that if you use them primarily for research they should fall under supplies.
Same with the museum costs, if you went primarily to research for your business it should be deductible.
As mentioned above, it's best to be as specific as you can without getting ridiculous. Say you're going through your purchases of stock to sell. In your notes you might have it broken down into each specific thrift, each auction by auctioneer, etc. On your tax forms you could just combine say "stock from auctions and thrifts" onto one line. Just keep your notes with your receipts and you'll be fine.
I think my breakdown goes something like this:
Stock
Supplies
Modem
Mileage credit
Donations
I don't use a Misc. category. Anything odd that doesn't fit in one of the broader categories would get it's own line. I'm sure some accountants will do it differently from others, but as long as the basics are there and the numbers are correct and backed up with receipts and invoices there shouldn't be any problems.