What can you use inside piping bags?

So I wan't to make a cheesecake for my boyfriends birthday, I've seen that a lot of cheesecakes and cakes have like the piping swirls on them? I bought a cheap piping bag today but I was wondering what to put in it? I don't want to have icing on it, If I whipped cream and made swirls out of that would they stay firm or go flat by the next day? really don't like icing, thank you :)