It's not really about the amount of stuff you want to talk about, it's just about knowing how to conversate.
A tip I've read from this site a while ago worked for me quite a few times. If the girl is very sociable, get her into talking about something, like a summer vacation, experience, etc. Make sure the experience doesn't bring in a depressing or saddening mood. So she'll be talking, and she'll take pauses to see if you're really listening to her. If she doesn't speak for 3 seconds, comment on something about it, like if she's telling you a story about her camping trip and raccoons snuck in their tent and almost stole their food, be like "so raccoons almost stole your food?". It'll get her to talk more, and keep on listening until she takes her next pause. Some people will make the mistake of following up with their opinion, like they'll say "so raccoons almost stole your food? Funny situation there." From my experience, after following up with an opinion, the conversation didn't really flow as smoothly compared to when I didn't.
While I said earlier it's not really the content that matters in order to be a good conversation partner, it's still very important to know about public matters, news, gossip, etc. People just place too much importance on this when other categories of conversation are more vital, stockpiling on things to say. Read the news, listen to friends when gossip goes around. I remember hearing about a shockbreaking break up at school during class, and these girls I briefly knew brought it up and I was brought into the conversation because I was on familiar grounds with them. It's great for rapport building.
Now the most important aspect of a conversation isn't what comes out of your mouth, but how your words are presented. Some people talk way too fast to try and fit everything they wanted to say or talk about a girl in just one minute. One reason why people run out of things to say. Take your time, it's not like women have a standard of the amount of things you have to say to them in order to have a good conversation.
Also, keep good eye contact. Eye contact is VERY important; it conveys whether or not you're confident in yourself.