Whirlwind PC-DI boxes come in handy for all those business meetings with laptops, I-pods, and mp3 players, oh my...
don't forget things like:
RJ-11 phone cables and couplers
RJ-11 to
xlr adapters, so you can route that phone line around the building or around the stage thru audio lines. And be sure to have your digital camera ready when your IT professional realizes what your doing....
RJ-45 ethernet cables and couplers
Video patch cables and couplers
Speakon to Speakon couplers
Headphones I would go for Sennheiser HD280 or Sony MDR-7506. Both are about the same price thru discount retailers. The Senn's provide better isolation in noisy enviroments and are indestructible, the Sony's are lighter in weight and fold up smaller, if traveling around. Sound wise the Sony's have a bit more high end in them, the Senn's sound a bit more natural.
-Bob