While I grab a shower whenever I can, I have used truck stops, baby wipes, local swimming pools (always have showers) during the summer, a larger town's indoor swimming pool, fire stations, sinks, etc. If I have gone more than 2 days without a "real" shower, I will get one mid-day even if I am doing more riding. While I like truck stops since I can usually do laundry also, I do not come across them very often as they tend to be next to major roads which I rarely ride along.
The primary place to keep clean at least once daily is the crotch and bottom areas. If they get infected (that rash that won't be fixed by typical monkey butt ointments), it is very painful and takes a few days to heal up after you have started taking the antibiotic.