Keep an eye for the coins which may appear in the fire. Tap them to add them to your collection.
If you create a flame over the spiders that scurry around a few gold coins will drop from them.
Some of the new objects will allow you to spread fire more efficiently.
Batteries are great for spreading fire around the whole grate.
Always check which combos you still need to complete by tapping on the icon on the top-right of the screen, then scrolling down the list.
Tomorrow Stamps will allow you to gain access to your new fuel much more quickly.