A very small note book with a pen for your purse or pocket, carry always in case you meet someone unexpected.
A large notebook for when you know you will need it.
A small tape recorder, even the video camera can be used as a voice recorder, if you have enough disks or film, the way to use this effectively is to ask them to pretend that they are talking to their great grand child, and telling them about their life and what they have done so far, this way you get a lot more interesting bits of information than if you asked things like when and where.
A digital still camera, this can be used the same as a scanner to copy papers or photos still hanging on the wall, but do a bit of practice at home first.
A copy of your family tree as sometimes people need a memory jog to get them started.
A list of questions who where when type.
there are many other things but this is a start
Bleggy