i use detol anti bacterial wipes...sorts em right out...2 mins of a job and you dont need to wash the car...just rub it over the relevant bit..
keep em in your glove box 
Just a quick note on that. Those wipes will most likely strip all of your protection of your body work so you would need to re wax after using them.
also aren't they likely to inflict swirls and scratches??
Best thing to keep in your glove box would be a bottle of Quik Detailer and a micro fibre cloth. If you have waxed your car and find some bird has done its business a quck spary of QD and a wipe over with the cloth will remove it in an instant
