Open it and find out.

The only thing left to do is to open that little metal box. First, though, you give a thorough look on the outside. It's a metal box, about three inches cubed, made out of some sort of iron or steel. The lid is a simple latch and hinge affair, there's no lock. The outside of the box has no decoration, it's just burnished metal. With a shrug, you open the box and look inside. Then you turn it upside down and shake it.

The damned thing is empty! Who just gives someone an empty box as a starting item?! The backpack makes sense, but what possible use is this? You're just about to throw it away in disgust when you realize that there's a new icon at the corner of your vision, beneath your status screen and spellbook. Focusing on it for just a second, it opens in your mind's eye and you are suddenly very glad you didn't throw the box away.

You turn the box rightside up again and look inside. Still empty. That's clearly some sort of inventory window, though, and there's stuff in it that isn't in your backpack. How to get to it, though? You reach two fingers into the box and pat around at the inside, but it just feels like an empty box. There's no potion ins--

As soon as you think about the potion icon with your hand inside the little box, you feel smooth, cold glass against your fingers. You grab it and pull your hand out of the box and lo and behold, in your palm is a small stoppered glass vial, about three inches long by a half inch wide, filled with a viscous, cherry red liquid. You check your inventory and the potion icon is still there. Is there a whole stack of these in there? You wonder. Setting the potion carefully on the ground next to you, you reach back into the box and think of the potion again. Instantly, you feel glass against your hand and you pull out another, virtually identical red potion. Setting this one on the ground, you repeat the process four more times. On the last attempt, nothing happens, and the box remains apparently empty.

So, you have five potions of some sort. Probably healing potions, given the general convention that healing potions are red and your Patron probably didn't set you up with a pocketful of tasty-looking poison after everything else they've done to help you out. The box itself is the bigger prize, though. Clearly the box can hold more than its exterior dimensions would indicate, and it also wasn't as heavy as it should have been with five vials filled with thick liquid in it. It's some kind of box of holding!

Eagerly, but carefully, you place the vials one by one back into the box. They disappear as soon as they reach the apparent interior of the box, and a thought comes to you. The vials are actually just about the same size as the box itself, and if they were actually physically present they would be sticking out the top of the box with the lid open like it is. Can you put anything inside as long as it will actually pass through the interior section? Casting about for something to test your theory with, your eyes fall on the spear and you smile. You place the box on the ground, pick up the spear, and carefully feed it in butt end first.

Hallelujah! This is the first thing which has gone right since you got transported here, wherever here is. Yeah, the spear takes up a ton of slots in the chest, but that was hardly unexpected. The big thing is that it works! It does look like a longer object might not fit, but how often are you going to need to drag around something that's three inches by three inches by ten feet? You pull the spear back out -- it's your only weapon and you have a feeling that you're going to want it close to hand when you leave this cave -- and then pull out the other objects from the chest. The leaf icon ends up being a stack of ten leaves that look very much like aloe vera, while the hamburgers are actually closer to sliders, and there are only three of them. They are piping hot though! Three hot sliders don't really a meal make, but maybe these are magical burgers of nutrition or something. Regardless, they're food, and food is something the old man made clear that you won't just find. The leaves, meanwhile, are likely the "soothebalm leaves" required by your Patch Wounds spell, though you hope not to have to find out any time soon.

With greatly lifted spirits, you put all your new-found loot back in the box of holding, and put the box in your backpack. Looking around the canyon, it's actually becoming really hard to see. A glance up towards the top shows that the sky has darkened considerably. You would like to give your Flame Jet spell a try and practice with the spear a little so that you don't stab yourself in the foot at the first sign of an angry gopher, but it looks like night will fall soon. Maybe you should get moving...