Thomas Jefferson's reusable "notepad":
In his pockets, Jefferson carried such a variety of portable instruments for making observations and measurements that he's been dubbed a "traveling calculator." Among his collection of pocket-sized devices were scales, drawing instruments, a thermometer, a surveying compass, a level, and even a globe. To record all these measurements, Jefferson carried a small ivory notebook (pictured) on which he could write in pencil. Back in his Cabinet, or office, he later copied the information into any of seven books in which he kept records about his garden, farms, finances, and other concerns; he then erased the writing in the ivory notebook.Via The Appendix and Erik Kwakkel.
Addendum: A hat tip to reader Walter Susong, who noted in a comment that modern versions of these are available:
"Based on an original that Jefferson owned. These are made of sturdy brass stock with 4 old ivory pages and a pencil. Use this for making notes in the field and just erase with a wet finger when you are done."