Here are the codes for the Blind Bag Mystery Hobby packs currently available from American Girl.
I don't live close enough to a store to be able to shop in person. I have used the codes before to check what was in the bag before opening. You can't return them once they have been opened.
I think the code is the last letter printed underneath the barcode. Well, printed is the wrong word. They are sort of punched in and can be hard to read.
A- camera set
G- pencil case
H- measuring tape