Clearing your sinuses is probably the best thing to do. Here in the States, we have this awesome stuff called Mucinex DM which just clears my head up completely without any apparent side effects. I'd suggest that if you can get it there. The active ingredients are Guaifenesin (600mg) and Dextromethorphan HBr (30mg). It's probably the guaifenesin that's the expectorant/decongestant, so if you can find something with just that you should be good. (DXM is a cough suppressant.) Otherwise, I'd just stick with a good expectorant/decongestant that you like or just eat a really hot curry shortly before you get on the plane (though that may cause other problems for the passengers around you besides just the germs).