I don't think it's necessary at all for you to clear off the counters before you drive off; indeed, in my experience, they're very effetively self-clearing while one travels! However, if you don't care to store your stuff randomly on the floor, then putting it away before departing is necessary.
Most things I just keep stored in cupboards, even when stopped for awhile. That makes putting away the few other things a good bit quicker. I will leave the odd dirty dish in the kitchen sink while en route and that has not been problematic thus far (beyond rattling around).