Take a bar of Ivory soap, toss it in a Tupperware bowl with a quart of hot water. Place bowl in sun, shake occasionally to completely dissolve the bar of soap.
You'll be left with a bowl of slippery goo. Saturate washcloths with goo, hang 'em on the line to dry.
Take a bag of dry, soap-impregnated washcloths with you. All you need is the water.
(Dump the rest of the goo in the pump soap dispenser in the bathroom, it makes GREAT handsoap).
A cheap Yankee told you that.