I am asking on a general base since I think answers might be useful for several types of characters, but if you want the details, I am currently playing a swashbuckler/duellist and I am not allowed to wear any armor nor shield, and not planning to adopt a two-weapon style. So since my off-hand is free, I was wondering what I could held to help myself.
At first, I thought about taking points in use magic device and held some rod or staff or other magic item, but I am not certain about which would be the more useful.
I also considered holding a +N dagger with the defending effect, which would give me a +N AC bonus. For example in A&E there is a defense dagger which is a +4 defending dagger with an immunity to flanking.
But I think I am probably not the first wondering on how to optimize this slot, so do you have any suggestion about this?
PS: for my particular case, allowed rulebooks are PHB I&II, DMG I&II, all Complete Xxxx books, MIC, A&E, eberron books, but if some funny suggestion exists outside those, I am also curious learning about it (might even manage negotiating it with my DM), plus I hope this question could be useful to other people as well, so don't feel restrained ;)
Thanks in advance!
EDIT: the question is maybe a little too broad, so to be clearer, I am looking at first for something that would make me more resistant, ideally something a swashbuckler is likely to held (and that the reason why I considered using a defending dagger), rather than an offensive tool, but if some item is well known being very cool to held, I might reconsider this approach, and this is why I tried to stay general in order to not orient the answers in a way that would make me miss a clever but a little off topic suggestion.