I certainly plan everything in my head, including what I'm going to say on any important occasion.
It's both words and images for me. I find the ability to plan like this is often time-saving and very useful.
Not so useful is another layer of sound which is exactly like standing in a crowded street and hearing snatches of conversation, not directed at me, as people pass by.
These can be different accents, male, female or child, loud or soft. It's happened all my life and I long ago learned to ignore it as they never speak to me at all.
In tandem with this are the mind-pictures when I close my eyes.
A Victorian street scene; a desert landscape; a group of schoolchildren - it can be anything and never related to an event in my real life.
Also, as another poster mentioned, I very occaionally get flashes of inspiration, especially about locating lost things or solutions to problems but somehow these are not words just a sort of 'knowledge' - and it's never wrong.
I once took part in a psychological experiment at a university to see how many things people could think about simultaneously.
Most of us can carry at least 2 threads of thought, as when we get an earworm song and are able to continue thinking normal thoughts as we go about our lives.
Some can get up to 10 different thought threads, I managed only 5 and that was a struggle.
The mind is a fascinating thing.