Thanks for your time (and of course I'll come see you there regardless),
Normally bookstores don't stop people from bringing books from elsewhere and they don't stop people bringing things that aren't the book. On the other hand, sometimes (not always) they will discriminate against people who don't buy the book from them -- people who didn't buy the book might get to be further back in the queue, for example. Or they might send evil clowns to your house to kidnap your pets. (I mean, it's theoretically possible. All right, it's very, very unlikely.) I doubt that B&N have decided what they're doing yet -- they may well only decide when they see how many people turn up for the signing.
If you DO buy a book elsewhere, it's always a good idea to bring the receipt with you, or if you don't have it, to make someone working for the bookstore give you something indicating you brought it in with you. It would be bad if you had to pay for it twice, after all.
The listings I see for your appearance here in Sheffield (at the
Univeristy Blackwells bookstore) says it is a "Signing"... Is there any
chance of a mini-reading?
Also, you mentioned gifts... but do you take baked goods? I don't know
about you, but if I were on the road for a stretch like that, I'd fancy
some pumpkin bread...
I don't know. Ask the bookshop -- it depends what they've set up. I'm always very happy to do a mini-reading and Q&A. Most bookshops like and expect them too. (They're a bit less likely to happen at lunchtime signings, as people have less time.)
On the whole, baked goods (cookies, biscuits etc) tend, at long signings, to be eaten by the very hungry people in line while I just keep signing...