since i hike my dogs everyday i always keep a case of 1.5 liter (trader joes) water in the trunk that i use for them and rotate out about every two weeks. as far as the tools are concerned, even though it takes more space, i use a cheap rubbermaid toolbox with basic tools(ie. cheap), duct tape, etc. and in a seperate container in keep extra anti-freeze, oil, jumper cables, etc. oh, and there's also a tarp, a beach umbrella, and some other stuff. needless to say my trunk is a bit crowded. but overall, it serves its purpose and i don't have to baby the stuff in there cause it was meant to be easily replaceable should someone break into my car. (a necessary consideration living in LA) basically, even though it takes up more space, it pays to keep tools, water, etc, seperated just in case. i guess it depends on where you live and what you use your car/truck for. my car gets a heavy useage. depends on the type/year of the car too, i drive a 14yr. old honda so keeping extra anti-freeze, water, oil, jumper cables, tow rope, etc. is a pretty good idea and has definitely come in handy. great thread topic.