[BigV]

My first experience with pressurized ketchup. We've had self serve pump style for some time around here.

As for the packets, when I am eating fries behind the wheel, or hash browns, or some other suitable ketchup carrier, I usually use this method. I cut/tear a small nick from the corner of the packet. I hold the packet with my left forefinger and thumb along the long edge, away from the side that has the nick. I can still steer with my left hand now, since I've only drafted these two digits for ketchup duty. Now I can take a bite from the food held with my right hand, putting it down afterward, shift my right hand to the wheel freeing my ketchup hand, and then bring the packet to my mouth and squeeze a little ketchup into my mouth directly from the packet. Chew, swallow, rinse, repeat.

This doesn't directly address the question of ketchup/carrier proportions, but it can help reduce waste and mess.