Depends on the marks, their location and purpose. I carry permanent Crayons, Sharpies, as well as paints and about four different sized brushes. Some of these are shown in the article about paint marking as well as a number of threads
Picture in this one of my paint box and some discussion. Then there are the 300 plus stamps and such in other nicer cases for organizational purposes
http://www.concoursmustang.com/forum/index.php?topic=6144.msg35109#msg35109remember it's best not to copy or borrow marks from other cars especially if they were built elsewhere, equipped differently and build during different time periods .
A discussion related to that and other general paint markings thoughts
http://www.concoursmustang.com/forum/index.php?topic=17466.15Was interesting to note (doing the search) that we've had 325 threads about paint marks on the site so far.