What did they do before on-board toilets? I was researching Jimmy Doolittle this morning, and I found this on History.com:


  To aid his record-breaking 1922 coast-to-coast flight, U.S. military
  strategist Jimmy Doolittle invented a funnel-and-tube-based "pilot
  dehydrator"—possibly the earliest airplane toilet.


That led me to the question: What did they do before 1922 when they felt like they had to go?
Go to the toilet before departure, and hope you can find somewhere to land if nature calls suddenly :)

Same really as before a long car journey today...

Of course aircraft of that time didn't have very long endurance, so the situation wasn't likely to arise that you'd need to make a pit stop to let nature take its course. You'd have a scheduled stop anyway well before that.