Try a penny. A very effective way to neutralize the effects of a Bee or Wasp sting is to tape a copper penny directly on top of the sting. For some unknown reason, the chemical reaction of your skin to copper nullifies the poison. The next day you will be hardly see a trace of the sting.
Any other suggestions for this apart from this method - don't go any where near wasps at this time of year - they are really grumpy people when the weather starts to get colder!