Can I combine fuels?

Suppose your fire of briquettes starts to go out and you have only a bag of charcoal left as a spare. It is no problem at all to then warm those up and add them to your fire. Do keep a close eye on the temperature and adjust it if necessary.

You can also add blocks of wood to a charcoal fire, but don’t do that when grilling directly. The flaring flames will then cause your meat to burn rather than cook. Barbecuing is done with heat and smoke, not flames.