Presuming cold water only- I like two systems for a simple kitchen setup:
1: Use an Aquatainer with turn valve mounted right over the sink. Gravity feed yet faucet convenience.
http://www.earthquakesupplycenter.com/a ... vengal.htm
2: Also use an Aquatainer or other 5 to 7 gallon portable container, but combine it with a draw tube and pump/faucet combo. A few brands of trailer use this option. You can either use a hand pump or electric. The T@B trailer uses this idea.
With either of these options you avoid the complexity of a conventional water system with filler inlet, vent tubing, etc.
Hand pumps: http://www.pplmotorhomes.com/parts/rv-p ... faucet.htm
Electric pump & faucet: http://www.racersrvstuff.com/racersrv/d ... EM=0291000
One neat feature of the electric pump that operates off a switch (instead of a pressure sensing pump) is that you can add a second "knee switch" - just a simple button switch located at knee level. It will help you conserve water.
I installed a permanent grey water tank in our trailer. It turned out being more of a pain than I imagined. Doing it again I would have a space under the sink to put a portable jug. That way you can still pull over for lunch and use the sink without draining on the ground or messing with a bucket. I suggest using a different type or color than your freshwater jug to avoid a yucky mistake.
Matching the fresh and grey water container size prevents overflow. I have 12 gallons for each, but even with two kids we use about 5 gallons per day not including showers. It's nice to be able to do a weekend trip without bothering with filling/draining water.
Again, this adds complexity. You need a hose, city water inlet, interior hose & fittings. It does give unlimited water. One of the hand pump faucets also has a city water connection with backflow preventer so it's not too complicated.
Unless you also expect to have sewer connection at the campsite I don't see much benefit if you're trying to keep it simple. Being able to use more water just increases the grey water production.