ok we just finished a sac for under encountering conflict theme. we had to write a personal piece based on our past experiences with any sort of conflict we've encountered over the duration of our lives, lol. it was basically creative writing, and in my experience the first sac is always creative writing, which sucks for me because i'm rubbish at creative writing.
coming up to the sac we did brainstorming exercises like discussing sources of conflict, emotions, resolutions etc. then we did planning stuff - 5 senses, the plot, constructing sentences, etc.
i don't know what you mean by there won't be a prompt :\ if you are suposed to write a creative piece then i don't expect there will be a prompt. you are creating your own story so you decide what it is you are going to write about.
in regards to the secret river you could discuss something like... moving, change of surroundings/environments, trying to cope/adjust to that etc. idk.