What to do when we get bored with girlfriend?

I'm 18 and she is 19 and sometimes we just get bored when we're at home. We go out for walks and stuff, but at home we usually lie on the bed and talk, but sometimes we just run out of things to say and just we just lie there in silence.

We go out to the city for a shisha or drinks, but fairly rarely. I don't drink coffee, so we also don't go to cafes like she does with her friends or did with her ex. Another problem is that wehen we go out, it costs money and I don't have that much.

The question is, what things could we do together? We still have fun and love each other very much, it's just that I don't want her to get bored.