Wax tablets are a nice, and very practical thing if you need something to write on. Unless you go into extreme heat, the writing on it will stay, and they are rather easy to make and easy to carry. If there's need for more space, a number of tablets can be strung together in a kind of little book. Very handy indeed.
In case you want to read some more about wax tablet finds in Pompeii, here's a little article about them describing a project made in Köln, and some nice images of charred wax tablet fragments.