Keep lot of slips of paper on a clipboard next to the bed. Give each idea its own slip (so they can easily be sorted later). Lay down on the bed 25 minutes early, which will give you time for the thoughts to arise, then you'll get your full sleep time.

I occasionally remember to keep pencil + paper by my bed for this reason, so that I can write such things down in the dark without having to get up or turn on a light. Even if the results aren't legible in the usual sense, I've almost always been able to remember what they were about in the morning.

I usually try forming a picture to remember all the things, then focusing on it very hard. You can locate a picture in a specific location to help remember it (method of loci.) As soon as you get up, write everything down. (You can "locate" it in your closet or somewhere you go right after waking, and that may help you remember.) This may have the added benefit of improving your memory.

You could also try to find a time earlier that you're not doing anything requiring thinking (like walking, or transportation, or eating, or whatever), and try to think of these things during that time, then write them down before you go to sleep.

I use my phone which I keep charged next to the bed.