I like to think I have a pretty good ear and memory (for music, at least). In my originals band, we took a few weeks off for life events and practiced last week. I usually have little problem recalling my parts, even months later. With the songs we did last week, no problem for me, but for my BL, he got a little twisted. He unwound his parts and was able to make it through, no big deal.
In my cover band, since we are covering 30+ tunes, there's so much more material, but it helps that in most cases, I've heard the tunes many many times (radio, tv, etc). I will practice to the original track with sheet music (if I can find it online), and then without the music. I refuse to use visual aids at practice, let alone onstage, because if I do, I can't memorize it. No shade to those that do need music or iPads, but for me, that's a slippery slope.