Some very nice pet food can be crafted, but it often uses items that are hard to obtain. The recipes are found all around the spiral, usually near the starting area of a world.
The fastest way to obtain good snacks is by doing Waterworks. This gets you good gear for level 60-90, so it's a good idea anyway.
If you've reached Avalon, several bosses will rarely drop Evil Magma Peas. Farming these will get you a mega-snack once or twice a week.
At the end of Zafaria, Mirror Lake grants you some good snacks along with decent drops.
