The Hero's GraveyardThis is a spot by the resting spot of ERC-003. If you continue to the left after reaching ERC-003's body, you will discover an escalator-type elevator. If you ride the platform up, there will be a patch of cave actually located in Yoyogi Park East that will ALWAYS have three gifts in it. The last one is usually a Portable Bed, while the other two can be anything from a Nail File to a Magazine. If you continue through the small path to the left, it will lead you to a drop-off that will pop you into Yoyogi Park East: that is why you can see a path on the map that you cannot access normally. Going back to the elevator from the Hero's Graveyard can kill you if you mistime it as you will fall off the earth.
It is possible to reset these gifts by running to a different part of the map (for instance, Yamanote Line West) and going back.