That's the great thing about it, use the bits you need and leave what doesn't work for you. I use the index sparingly, to make note of things that I might need to reference later but might be difficult to find. I usually do this at the end of the month before I store the book away. The future log and calendar are just there in case I need to write down a date and don't have my phone handy, because I, like you, use my phone's calendar because sometimes I need push notifications. If those thing are truly useless to you, leave them out. It took me several iterations to find the ideal setup for myself, I started out with all the things and dropped what I didn't use, went to a small book for ease of carry, now I am never without my little external hard drive. Check out the Little Coffee Fox site for a more artistic take on bullet journaling. If you don't see something that suits your needs, make it up!