Designer items like a notebook (or other small item form) show you have class and taste, and more importantly: attention to detail, which is often something appreciated at jobs. I see nothing wrong with bringing your Coach planner to the interview - I know many people that have bonded with new coworkers/bosses over things like that. You just never know who you will be meeting, that's all I have to say about that.
It's funny because I just went to a job interview (been a sahm for 11 years) and only have my Carly.. so I took it... when I met with the man first thing he said is "nice coach bag!" I told him he was a man I liked and he said his wife has nice taste and he knows a nice Coach bag when he sees one.. it was fun and broke the ice!
LOL...see? My point exactly! You never know!!!!
My boss is a lifelong aviator and more into boats and fishing and such, but one day he told me he keeps his wife in Louis Vuitton...then one day he came to work and said he went to Coach and bought her something after looking at all my nice bags!
So it can be a benefit and a way to bond with people without knowing it! LOL!!!!!!
The way I see it, it definitely cannot harm you unless your boss is someone that abhors materialism...