Open config/client/config.cs.
Every line beginning with moveMap.bind( has three parameters. The third one is a function name. Any function listed there can be called with functionName(1) to simulate the bound key being pressed, or functionName(0) to simulate it being released.
Every line begining with moveMap.bindCmd has four parameters. The third is what to do when the key is pressed, the fourth is what to do when released.
From this list you can discover jet(), jump(), crouch(), and countless others.
However, it also shows how to create custom commands. Note that you enter these in the console, and then they will automatically save when you quit. How about
moveMap.bindCmd(keyboard, "ctrl j", "Canvas.PushDialog(JoinServerGui);", "");
To quickly review the server list?
And perhaps you may find
moveMap.bindCmd(keyboard, "alt j", "", "jet(1);");
useful, to turn jets on, and leave them on, without requiring you to hold the mouse button down.
Note that this is the absolute worst way to add a keybind, it is best to use the proper route of adding it to the configuration menu if you are writing an add-on, however this method is useful for quickly adding a button mid-game that only you will ever need/use. If you actually plan on releasing anything, please, do it right the first time and just add it to the option menu.