I've had this dilemma with packing protein powder along with me in a ziplock bag on past trips. If they are suspicious of your baggies of Epsom salt, they will test it for any illicit substances, which will show that it is just salt and you'll be able to keep it. You have nothing to hide, so I wouldn't worry about it. They could confiscate it, but that wouldn't be too bad in the long run, it's just salt and you can get more salts at Basin in DTD (I think we got a coupon for Basin in our Mickey mail last week along with our DME luggage tags, etc).