Don't use the Upgrade Altar on level -45. Keep the money for upper Zones.
Collect all Red Gems. Collect Blue Gems if you have plenty of keys.
Collect the Bomb later. If you have ~700 HP and 27 AP you can fight the boss battle without the Bomb. It will be much more useful in upper zones.
If you have to fight the Earth Elemental, wait until you've collected all the AP you can. This is a good guideline for most elite monsters in most Zones.
Merchants in this Zone sell a Blue Key for 50, a Yellow Key for 10, and 5 Yellow Keys for 50.
The Altar room on -45 contains for sale Bomb, Magic Mattock, Scroll of Teleport, Scroll of Height, Golden Key, Water of Life, Wand of Flight, Crystal Ball, Vampire's Fang, Lucky Coin, and Ring of Antimagic.
Once you have the Scroll of Earthquake (purchased in the 5th Zone from a vendor or the Level -15 Altar room for Soul Stones) return to floor -49 and use it to destroy all of the walls to reveal the guard and pommel to the Fire Blade (hidden in secret passages). Alternately, you can use two Magic Mattocks: one on the top left block, on the wall furthest left, and one on the top right block, second wall in from the right, then keep pressing on the walls to reveal the secret passages.