http://www.thetoolwarehouse.net/p-6337-solar-es5000.aspx These work great for jumping a/o boosting car batteries. Used them all the time at the auto shop I worked at. I carry one in my pickup for emergencys and to power up accessorys with a cigarette lighter adaptor.
Use low viscosity motor oils in winter. If you keep a low amperage charger hooked up to the vehicle battery it will keep the battery warm for cold or very cold starts. You can also get battery warmers that attach to the side of the battery, they have to be plugged in to 120volts.
Service your battery and cables to make sure you have very good clean connections. You can buy battery terminal anti corrosion sprays to seal terminals. Don't use the felt rings, they are too thick and won't let the cable clamp down far enough on the terminal. I use grease in a pinch. You can also buy universal battery cable covers to cover up the grease to cover the mess.