How about the windshield washer tablet from 303 products? I use them and they work great. If you are in a climate where it doesn't freeze, just add the tablet to a gallon of water. In the product, you purchase 5 tablets at a time, so you have five gallons of fluid ready to go at a moment's notice. I live in Colorado (read: it can get real cold), thus I add them to the cheap blue stuff and it works great.
Here is the info on the product:
"Super-concentrated and especially formulated to completely remove road film, dirt and grime leaving windshields sparkling clean. Non-toxic, biodegradable and engineered safe for rubber and paint.
Each summer 100 million empty gallon bottles of windshield cleaner are trashed, cluttering up our nation's landfills. 303 Instant Windshield Washer Tablets mean no plastic bottles to dispose of. Each super-concentrated tablet will give you up to a gallon of unbelievable cleaner power.
Formulated to completely remove bugs and road film, "303" tablets can even be used in the winter months with any anti-freeze windshield solvent to ADD cleaning power those products lack. Stores in your glove box. 303 Instant Windshield Washer Tablets... we supply the cleaning power, you add the water."