You'll want to explore a little more. One of the boars outside to the right has an item you need. There should be enough items to get you through: if you're running low, you might want to double-check you collected everything, or possibly just do a fresh run, since you're near the beginning.
I think you probably ended up doing that first bit in a sequence I wasn't anticipating. But if you get all the items in the office and in the warehouse, you should have plenty to deal with both the encounter in the warehouse and the boars you need to defeat outside, at least to get the key. Remember you can heal via skill when out of combat, you don't have to use an item.
Also if it helps, the boar with the key isn't randomized, it's the same one each time. So if nothing else you should be able to save-scum until you hit the right one. With the above though, hopefully that won't be needed.