I imagine that I am not the only person that hikes or backpacks with allergies, so I wrote up a little wiki article about dealing with allergies. I am definitely no doctor, so talk to a medical professional if you have any questions. The article is based on what I have gathered from my many sinus doctors thanks to 15 years of serious sinus problems (a few surgeries, several procedures, allergy shots, blah blah blah).
Maybe this will help someone avoid the sniffles. 