If I drop a stitch while I am knitting and don't have a crochet hook how can I pick up the dropped stitch?

You could use a darning needle if you have one. I actually prefer to do it that way. If you don’t have that, I think a sharpened pencil would even work.

I’ve done it with another knitting needle.

I usually use two short dpn’s – one to pick up the dropped stitch and the other to “knit” it back.

You could probably fashion a fake crochet hook out of a paper clip. It wouldn’t work if you actually needed to crochet, but for a dropped stitch, you should be fine.

I also have used another knitting needle.

By listening to Donovan? I think the instructions are in the song Season of the witch?
*I’m kidding… I have no idea, I crochet, I’m jealous of people with the brain power to be able to knit! It’s hard