If you had asked me ten years ago, whether I find the keys we are going to talk about in this post any useful, I would have said NO. But ironically, I use them quite a lot these days and I cannot live without them as well.
Home and End Keys
If you program or do document editing a lot you will understand the importance of Home and End. There is no quicker way to get to the start and end of a line.
Ctrl + (Shift) + Left/Right Arrow
Ctrl + the arrow keys, can be used to move over words rather than characters. Can be really useful for programming and document editing. I cannot live without this. Just makes navigation faster and easier.
Using Shift along with this combination helps you select words rather than selecting characters as is the case with Shift + Arrow Keys
Again, for people who handle many lines of code on text editors and huge documents, there are no better friends than Page Up/Down. Scrolling can be the most annoying thing sometimes on the mouse and these keys work like a charm in these situations.
F2 is one of those keys you cannot live without whether you are browsing files in a file explorer or working in an excel. F2 can be used to rename a file or edit a cell swiftly. It is very handy.
Ctrl + Shift + T
This combination is extremely useful on browsers. They reopen closed tabs. The function may prompt you to ask if this is really that useful, but once you start managing tabs in the order of 10 to 15 or more, you will start realizing the need for it.
Those would be my top five. Of course the obvious ones like Ctrl + S for save; Alt + Tab for window switching; Super + L for locking the pc and just the Super key for entering into the search menu on Ubuntu are really important too. There are a lot of shortcuts that pertain to specific software and are really useful, but I wanted this list to be as generic as possible.