1. This pink bathroom (via Retro Renovation) from the late 1930's is pretty close to what a lot of us probably grew up with. But what is that tiny sink for? Brushing your teeth! It's a dedicated "dental sink." I guess people figured there would be less risk of germs spreading if your hands and your mouth didn't share the same sink....not a bad idea, now that I think of it.
2. This second bath (via Create and Smile) from the turn of the last century seems pretty self-explanatory, except for the small flat-topped tub in front of the sink. Believe it or not, at one time a foot bath was standard-issue for every indoor bathroom. Why? Even with indoor plumbing, people didn't bathe every day and a tiny foot bath used less hot water to freshen up after a long day of work.
3. Finally, this last early bathroom illustration (via 1912 Bungalow) from the Standard Plumbing Supply Co. includes a sink, a tub, and the previously mentioned foot bath (presumably the toilet is out of sight). It raises the bar with a cage shower--where water is forced through the pipes of the "cage" and you get spritzed from all around--and a sitz bath. What's a sitz bath? It's kind of like a bidet, except you submerge your lower half in the tub and soak. I can only imagine this was another hot-water-saving feature like the foot bath.
So, as you can see, we've really pared things down over the years. Most of us would consider a bathroom complete if it had a toilet, sink, and even just a shower, so maybe the tub is the next "standard"-issue fixture to go. What do you think? Could you live without a tub? Which formerly standard fixture would you like to see have a comeback?