To explain, I will usually read one fiction book at a time but I will easily give up/abandon a book that doesn't grab me and come back to it after I've read something else if I feel like trying again.
During this time, I can also do a non-fiction book at the same time if it's for work.
There are exceptions to the one-book-at-a-time.
If I'm traveling, I might have an audiobook for the car ride that I'll listen to when I'm driving but a paper book for when I'm just sitting around and reading.
Ideally, I'll try to get the same book in both formats so I can read while sitting and then switch to listening to the same book when I'm driving around. But if I can't make that work, then there will be two separate books.
And if I know I'll be waiting around in many places where having a big book will be inconvenient, I might thrown an ebook from the library on my phone. That's my least favorite way to read so I will normally have a very easy read on those. Maybe something chick lit.