Measure the instant coffee into a spice grinder or small food processor, process until it's a very fine powder.
Measure your milk powder, Epsom salt , baking soda, cinnamon, and nutmeg into your plastic baggie. Add the coffee to the bag as well.
Press most of the air out of the bag, and close the zipper on it.
Manually crush any clumps in the salt, and work to combine the ingredients.
Transfer mixture to an airtight container, or measure into bath tea bags. Filled bath tea bags should also be stored in airtight containers.
To use, measure 1 cup of Pumpkin Spice Bath Salt - or throw one bath tea bag - into a hot running bath. Rinse after use