Outdoor Growing By a Creek

If I really can't be there more than once a week, at best, how close to a creek or stream should I plant so that I don't have to water?

I really doubt your plan will work. Either the ground is dry, or its too wet. Your plants need the right amount of watering usually to survive. Even if they are grown outside, sometimes mother nature alone cannon keep ur babies alive, i.e. droughts, too much rain, no sunlight etc. the chances are u'll need to be there a lot more than once a week. lots can go wrong in 6 days.

On the bank. Planting next to a creek wont make much of a differance, you only have about 10 to 20 feet of saturation from the bank. I use to put 2liter bottles under the ground up to the cap. If you poke small holes in the bottom of the bottle and fill them up after you water the ground it will slowly leak out giving you 3 to 4 days worth of extra water before having to return. (fill the bottle and put the cap back on.) I would put 2 or three bottles around each plant. Hope you find this helpful.