I also keep spare cards around. I bought a bunch of the 512 meg when they were on sale. I think I paid like $2.36 a unit with free shipping.
I keep them in the case I bought for $11 that is zippered and holds my jetbook, memory card, pad of paper, pen, and my book light.
The Jetbook is held in with velcro and the book light attaches to the same velcro strip on the back of the Jetbook. It keeps everything in one place and still fits in my coat pocket.