I made 5 of these journal jar's for Christmas gifts this year. I forgot to take pictures of them, so this is courtesy of my friend Jessi who received one!
What I did was type up a ton of journaling prompts/questions, printed them on fun colored paper, cut and folded them, and tossed them in a jar.
When they run out of something to blog about, they can take a prompt from the jar and then blog about it.
Or you could also give the jar with a journal and they can just paste the question in the journal and write their answer.
I made one for myself, but never finished it. I just have all my questions in the jar but not decorated.