when you start the demo, buy the pickaxe & lantern in the house to the left of dark cave on route 31. then grind up your mining lvl to 20 before heading to the professor with the letter, the reason for this is you can sell everything that you mined at the shop in NewBark Town
after you have talked to the professor in the lab you will be able to mine the rock that is to the left of mr Pokemon house which is a shortcut to it. this also comes in handy later on
after you have talked to the professor in the lab you will be able to mine the rock that is to the left of mr Pokemon house which is a shortcut to it. this also comes in handy later on