The only real way to get hobby projects is to find a problem you've been having and solve it. So what are your problems? :-)
Here are some of mine, that I turned into Go code: (restricted to "week long hacking" or less)
A simple blog application.
A command that when run, sends the output of other commands to your email.
An image viewer.
A simpler interface to `xrandr`.
A parser for the new TOML configuration format.
Or, you could pick a small program that you wrote in another language and port it.