This is gravity or water pump, fresh/grey/black water holding tanks, and a sink.

 
Pros: 

• You can stealth away as long as you're not dropping Taco Bell bombs too loudly. 

• Easy for emergencies, super rural areas, being in the cold. 

• Water on demand, and depending on your tanks, a lot of it! 

• Can easily build a shower inside (space permitting). Skoolies, RVs, box trucks will have the most floor space and standing room. Vans curve inward and eat that livable footage up. 

Easy to obtain, no installation required. Easy to replace, dump, and fill.
WIth the ones pictured there are usb rechargable pumps for them. Just set it on the floor, hook up the pump and you have potable water. Refills range from $0.50-$1.50 in my current location. Initial cost from $10-14/each.
The squared ones are also known as jerry cans sometimes, and prices range wildly. They're easier to store side-by-side and lash down/build shelves over. You can mix and match, too. 

 
Pros: 

• Definitely recommend! You can get grey water tanks, it is frowned upon to dump out onto the street or into the sewers you're not paying for. Some places are more camper-friendly than others and allow dumping. 

• They're cheap!

• Don't need a water pump or heater (temperature permitting).

• Easy to share, throw it on a table/bench for easy outdoor kitchen. 

Relatively cheap. Will need installation and even weight distribution if going on the top of your vehicle. 

 
Pros: 

• Easiest way to work in a gravity-fed shower. If you get black pipes, it'll warm the water and reduces the need for a water heater.

• They're also cheap!

• There are food-safe pipes available, so you can use for potable water as well. 

• Easy to refill. Drill a hole and plug with a removable cap. I've never had these, but would recommend cleaning and sanitizing regularly if you're going to eat out of them. Mold and bacteria can get in while filling and emptying. 

Butt....where do you GO?

 
Full plumb - You will have it all in your rig. Filling, dumping, and cleaning your tanks is on you, Hoss. Convenient and stealthy, great for long-distance and longer term dispersed camping. 

Cassette Toilet or Composting Toilet - These are both good options. The mileage will vary. RV toilets can be bought for relatively cheap. You will need to get comfortable dumping, maintaining the bucket/cassette and possible smells. It should be put somewhere it isn't going to tip over. You can build a little nook for it that can hide it while keeping it secured. Composting toilets can be DIY'ed, or purchased for around $1k or more. They separate the solid/liquid waste and have very little smell and easy to maintain. 

Stores - While you're on the road, easy at gas stations. When parked, 24hr stores are good if available. General rule of thumb is to purchase something and not leave a mess. 

Campsites - Parked for the night? No matter what, you will have options either in a pit/vault toilet or plumbed facilities. The TP supplied is generally 1/2-play tissue paper or the kind that's on the BBQ spits and lets you tear off a thumbful at a time. Bring your own. Go in peace. 

Basics: Need fresh water. Something to rinse. A place for the dirty water to go. 

IN THE RIG: All of the water options above will give you a base to bathe with.
      If it's not gravity fed (mounted roof pvc pipes, put a 5 gallon up high)...

• Get a pop-up single person tent for camping to shower in

• Fix a shower curtain to the back or side of your rig

• Hook it up to a pump

• Using a battery operated pump

• A garden sprayer (manual hand pump)

• Marine foot-pump (manual)

• Use a separate bucket, for wash, rinse, then dump safely

• Spongebaths

• Dude-Wipes or baby wipes

• Camp showers/solar showers (usually  a bag  which is gravity fed).
  
  
  
  OUT OF THE RIG:  Less mess, and save your water/electric!
  Expect to pay for all of these, rates will vary. I've left off obviously expensive things like getting a hotel room or airport lounges.

• Truck stops, bring shower shoes. They are much much cleaner than people presume! Usually will be timed and you wait til your number is called. Ask the clerk about using them.

• City facilities, gyms specifically have been the cheapest at $0.50 and are pretty quiet if no activities going on. Use the facilities, too if you've paid for it! Open court basketball? Cool, head to the showers or ask if you're unsure if it's okay.

• Gyms. All. Kinds of gyms. Not just planet fitness. I've found them at boxing gyms, climbing gyms, tennis based gyms (courts?), city gyms. I'm sure there are others, but those happen to be the activities I do. Think outside the box!

• Natural hot springs (some free or cheap entry) but usually required to shower prior to entering to not disturb the happy little biomes. 

• Beaches

• Campgrounds

• Hostels