Torch

Torches are often your best friend as they serve multiple strategic purposes.

You often get plenty in the dungeon, normally there is no need to buy them from the starter shop. But if you want to buy them, it may be cheaper to buy one tool for 5 gold and then use that tool to remove several torches from the walls of the dungeon. (specially true if you play rogue with +1 nimbleness ring)

When lit, they can be used as a low attack weapon with a nice knock back, useful to kill bloats or phantom blades (that only have 1 HP).

If you are playing a run "naked" starting with nothing, this may be your first weapon.

You can also throw a lit torch on vegetation to start fires, often doing massive damage to near by enemies.

You found a locked chest or trapped chest? No problem, pull it near vegetation and lit the vegetation on fire along with the chest. After the fire, loot the items. :)

Also useful to remove flammable gases, to make the area safe for walking. Place a lit torch next to a gas vent so the gas burn right there and does not spread near you.

Torches can also be used to scare some enemies away: bats, rats, wolves. All fear fire and run from it. Some trap rooms are full with baths or rats and can be easily done with a lit torch in your hand.

Torches can also be used as a distraction, turrets will ignore you and focus on a lit torch that lies on the floor. Goblings also stare or pick torches (playing with fire) and will mostly ignore you.

You can obtain torches from the walls by using Tools on them.

You can use a lit torch to fire up braziers and torches that are turned off as well as to lit sacks of gun powder or bombs that are laying on the floor.

Throw a lit torch on the floor and then lob a flask with gas or poison gas to light the enemies on fire. Or throw gun powder or bombs on top of the torch.