I'd leave the knife at home and carry the water ;-)
If you haven't bought a knife, chances are you don't need one. You'd have bought one already otherwise. If you're going to get one, get one you'll carry everywhere. I'm guessing you're not going to carry a 2' machette down to the mall. Or even out of the truck. Actually, you probably won't carry anything that isn't a folder. A folder will slip into your pocket, and weighs nothing. You can carry it everywhere they don't have metal detectors, and nobody will notice. Get a spyderco. You can't cut a forest down with it, but I'm guessing you've got a chainsaw. I'd go for a delica, or a centofante. They both have the nice balance of being small and light enough to carry every day, large enough to be useful, and sharp enough to do everything form open a letter to dice a tomato to feature in a steven seagal movie. The price is about right too.
Shaun