Typically use the cap that came with - fill with ro water and put it on the probe. If you don't have that, then creativity with glad bags sealed with packing tape can work.
Yep, I've shipped probes with a bit of wet paper towel (RO water) in the corner of a ziplock bag with the probe stuck down in it. Then wrap the bag around the upper part of the probe and tape of rubber band it to seal it.