So you'd like to use your DS as a notepad. You could
- write stuff in Pictochat and keep your DS in sleep mode until you get home
- get a flash card (not necessarily just for this) and use DS Organize, or
- stick a bunch of tape to the top of your DS and write on it in pencil
If the final option sounds appealing to you, check out this Instructables guide to "modding" your DS into a notepad. We actually kind of covered the whole elegantly simple process in our description, but you may need more detailed instructions. Apparently Scotch Magic Tape is, in addition to being sticky, an excellent surface for writing and erasing with pencils. Thus anything that can be covered with a layer of it, like a DS, can be made into a notepad. That is, anything light-colored enough for pencil lines to be visible -- sorry, Onyx DS owners.