My FAKs always have a topical anti-itch cream, like Cortaid. That's my top choice. Calamine relieves the itch but doesn't, in my experience, work as well, as well as being bulkier to carry, so I don't carry it. An anti-sting med like a bee sting swab is a good next choice for temporary relief. Last is Neosporin plus pain, it works better than nothing and I always have some, but it's not great for this.
good advice. calamine is the 19th century approach, using a clay base to absorb the oils which cause the rash. These oils are present in the exudate from he blisters that form, so contact with the exudate will cause further blistering. The active ingredient is the oil, and removing the oil is best accomplished with soap or dish detergent and water, lots of both; other non=polar solvents-gasoline, alcohols, wd-40 might work but have some inherent hazards of their own. Nasty stuff. Topical and systemic steroids, and antihistamines are the state of the art in treatment.