Computing and telecom are obvious. By 2050 it's fairly likely that a majority of the entire population of the Earth will own a computer (e.g. smartphone, tablet, or pc/laptop), which is pretty profound if you think about it.

Fulfillment will be a place for fortunes to be made, as it always has been. Amazon has been executing exceedingly well in this area but it's not as though everyone else has been sitting on their ass. Over the next decades the sort of smart, high-tech, low latency fulfillment that we've come to associate with Amazon will be the worldwide standard anywhere and everywhere. Also look for infrastructural improvements along those lines. It used to be that people had visions of pneumatic tubes running everywhere. But consider some variations on that theme, a fully automated delivery system that could route standard sized containers across cities, continents, or maybe even the world. Maybe autonomous vehicles could play into that, but it seems as though building custom infrastructure would also provide a substantial RoI. Imagine how different the world would be if every housing structure had a 1m^3 "mail box" that you could receive packages in or send packages from which would immediately deliver them anywhere in the system 24/7 without human intervention. Economics changes a lot, consumerism changes a lot, industry changes a lot, and so on.

Fully automated manufacturing and configurable manufacturing. These may not replace all manufacturing but they seem likely to me to become a "big deal", and people will make a lot of money off them. Imagine if you could go to a web page upload a bunch of plans (3D models, wiring diagrams, etc.) and place an order for a factory to manufacture something you've designed. This is more than just the home manufacturing (3D printing et al) revolution, it's something on an entirely different scale. Imagine how this sort of thing would affect the cost of production of material goods. Imagine how it would affect the iteration speed as well. And think about how it would affect the mass production society we've grown accustomed to. What happens when a designer can produce a batch of a few hundred or a few thousand custom designed smartphones or what-have-you? Instead of everyone buying from a small pool of mass produced goods does the market change to focus more on boutique versions of such things? Do people start buying things that are more customized in functionality? What happens when you create factories that can effectively replicate themselves?

Education is slated to change dramatically over the next decades. Much of the world today lives in areas where formal education is not the norm. As those areas become developed there are education opportunities other than the traditional ones, especially when you consider the widespread abundance of computing devices in the future (see above). There is a huge market for learning software, on a multi-billion dollar per year scale, but a hell of a lot of work will have to go into creating all of that software to make it effective and practical.

Space will be big business too but that can be a bit hard to predict. Through the 21st century the cost of launching things into space will drop by at least a factor of 10 if not a factor of 100 or more. That will cause an exponential increase in the amount of stuff and people we put in orbit which will create substantial off-Earth economic activity which will gain momentum due to positive feedback effects. By 2100 I'd expect millions of people to be living off-Earth and trillions of dollars in revenue to be involved in off-Earth commerce and industry. This starts to get really interesting when you consider what sort of potential advantages building things in space might have. Obviously it makes it easier to test spacecraft, of course, since you have access to the environment they'll operate in right there. But there are also some other interesting aspects. Vacuum is abundant and easy to get at. As is zero-g or nearly any level of g-forces you desire. A lot of manufacturing processes would be very different if vacuum conditions were cheap and easy to get at.