Lately I decided to try out the Prickley Bear Cactus plant. My results were amazing :O at mature they can commonly drop their own seed (allowing you to multiple your amount of them the more you plant) and they have a good chance for mega snacks (+25 xp) at elder.
Best part? They are FREE! They drop low level snacks for selling (about 150 gold or more each) if you need to refill your gold after buying multiple.
While Magma Peas are nice, PBC is really effective as well
Couch Potatoes are farmable from low level street mobs in Savarstaad Pass, I have hundreds and never bought one. They are low maintenance on needs, always give mega snacks (+40, 45, 50), give loads of TC and regular snacks to sell for masses of gold.