How do I keep a conversation/small talk going and not get an empty head?
Depends - how far into small-talk do you find yourself running out of stuff to say OP? Is it from the very start, or is it after the general "so what do you do with yourself?" kind of questions.
Not everyone can small talk easily.
You should let it flow, maybe pray the other person is good at small talking. But don't fall into the "I suck at this why do I even try" abyss when your head gets empty.
Relax. The other person is also trying to think something to say. Silence is only awkward if you seem bothered by it