What conversation topics should I use when texting the girl I like?

I like this girl in my cl and she has told me that she likes me too but we are not going out or anything. We see eachother in school everyday and we text eachother alot too but sometimes I get stuck for things to say when we are texting and the conversation can sometimes be a bit uninteresting. Can you please give me advice as to what conversations I could have with this girl or funny things to say. Anything that would make the conversation interesting! Thanks!