***SPOILERS***
There are definitely more secrets, but I don't think there's any that are quite as secret as that dagger. As a rule, check out the walls for secret buttons and such as you explore. Some walls can also be walked through, or smashed.
Many feel that the dagger actually makes the game too easy early on, but those Shargas are pretty tough. One thing that can help actually is moving around a lot during battle. It seems weird at first but quickly turning around and then backing away from the enemies makes it harder for them to hit you, and you can throw things at them in the meantime. If you've found any arrows, you can actually throw those at enemies to do some decent damage. Otherwise you can throw rocks, and often hit them a few times with a melee weapon as you're turning around, or as they approach you from a distance. These tactics, combined with eating healing items, makes these guys beatable without the sharp dagger. You'll find some nicer equipment soon too that makes combat a bit easier in general.
I can say that with that dagger, you won't find a better weapon until MUCH later in the game, which can make finding items less fun than it would be normally.