Well, if there is one thing I've never really struggled with, it was creativity. I don't mean to brag or anything, but I've never had a problem creating new material that is radically different from anything I've ever made.
In fact, I should note, that the only times I've ever felt stifled with my creativity was when I was studying a specific player. For instance, I was a huge jaco nut a couple years back, after a while I found myself almost subconsciously playing like him, and no matter what I did I kept going back to 'jaco' styled riffs. This happened with michael manring for me as well.
Now, the interesting thing about that though, is that through studying(and getting a little obsessed) with these players, once I finally broke away from that "gotta play like X" mentality, I suddenly will find myself occasionally playing something that may remind me a little of manring or lawson or duck dunn or whoever my favorite bassists are at the time, and it doesn't bother me because it's authentic, it's become a part of who I am and I'm not faking anything.
The actual creative process for me is infinitely varied. However, I have found that very often I am inspired by sounds.(this is also part of the reason why I love the bass so much, it is so versatile with the sounds it can create) I'll hear a sound that is really interesting, or unique, or just fun to listen to and I'll want to utilize it to make something neat. Often times, what may begin with simply working with a specific sound will end up not even using the same sound that I started with, but it's okay because it's not so much about specifics, it's about where you go with it and what it says.(imo at least)
I do go hiking a lot, and that does provide a certain calm of mind that I can find relieving, I can't really say it directly influences my creative process, but It certainly doesn't hurt.
There is another thing though about creativity, and that's a tendency a lot of people have to setup roadblocks for themselves. Where maybe "I'm not creative if I can't make a new song every week" or "ugh! I can't get this part to fit! I'm not creative enough!" That type of mentality is very counter-productive and it helps sometimes to take a step back and consider the bigger picture.
Shrug, this is all just my opinion, it's not necessarily right or wrong, I don't know if anything I suggest will work for you, but, it can't hurt to keep your eyes and ears open to any new ideas, you may find that is what stimulates your muse.