So far, since i started playing, i've simply accepted all missions as i went, just so that by the end of the generator missions i would usually have completed 2-3 of these. I've also found that having one pet very high leveled and a few more at the ready is a good idea as when the high leveled one dies, or you go into a dangerous area, you just swap out. The frost scorpions are your best friends once you can get one as a pet. As for just training, i always just stuck around to beetles, that way you can take a pause in between to heal up, plus you can leave your pet behind or do anything to practice.
When i just started off, i just kept killing blue beetles (sand i believe they are) until i had plenty of shells, berries, gold and such so as to be able to pay for supplies.
If you insist on buying food, the most conservative kind is the leaves (15g each). Healing 20 health each, you only need to spend 45g to heal the same amount as one small potion. This way, even though it takes extra time to use it, it is still more than worth it.
~~GemMaster~~