I see the whole clients on upwork not paying you a real trend, thought it was just me, highly annoying but hey what can you do?
If you have digital marketing skills its pretty easy to make a living travelling running adwords campaigns for companies, social ads, display or remarketing or just creating banners for ads or emails you'll be suprised at how quickly you can get microtasks and bring in the cash.
For me the biggest pain is the different payment methods if you're using Escrow or Paypal then having to send your money back to your local bank account and then having to pay fees to draw it in the country you're in is frustrating at times
Also if you're travelling and have a a decent camera with you, snap a few shots you find interesting and add it to stockphoto websites. You may not get paid immediately but put your content out there and sometimes you can get a sale or two
@chekohler, yes, you can dispute it, but it's hard, try keeping all conversations on Upwork or email, not Skype, so you have something written from them and make them sign a contract.
I didn't think of adwords campaign, it's a good idea :)
I know, the fees are making it all a bit more difficult, there is transferwise also, which now charges less than Paypal.
It's all such good ideas you have:)! Yess stockphoto sites can be awesome for passive income!