Sometimes our brains fail us and we just don't feel very creative. Fatigue can strike even the most enthusiastic of F/LOSS contributors and there are a number of ways in which it can be combatted. However the one way I find works for me time after time is simply to 'code for the lulz'. The Internet is full of doing people who do stuff for short-term amusement so why not bend that approach to productive output.
When I can think of nothing better to do, but I've promised myself that I will lay off Minecraft for the week and I've reached my social-media saturation point, I often find myself sat at an empty editor window pondering what I should write.
This is the perfect time to learn a new programming language, or have a go at something entirely un-related to projects you normally work on. For example, once I was so fatigued by my project to write a web application framework that I instead learned how regular expressions work and wrote a thorough implementation of regular expressions (and through that, DFAs and NFAs) which I have subsequently never used. But I had great fun doing it and learned an awful lot about how to write regular expressions which will be evaluated efficiently.
I'm not entirely sure I'll ever use the understanding of finite automata that I gained, but I sure know I had a crazy amount of fun writing that awful code. Sometimes all you really need to do is take a step back, pick something odd, and code for the lulz.