I had similar happen... A friend recommended regular crayola markers. They've worked perfectly! I also carry a small size versafine black inkpad-(love the hinging lid for on the trail) along with a small gold and silver (just because you never know). For concern about color/ink drying before getting to stamping... just huff the stamp before you stamp it. Works a treat ;) (for me anyway)

along with a small gold and silver (just because you never know).

You might want to rethink using metallic inks on stamps that belong to someone else (unless the clue suggests that you do). I have seen many complaints and requests that finders NOT use metallic inks because they are too hard to clean off, and will transfer off in the next stamping, thus contaminating the ink pads of those who follow you. FWIW

Wow. I honestly had no idea and now I know.
Thanks!