The idea with encumbrance is that you as Referee (and as a player) quite easily can make estimates of the encumbrance of something. My desklamp for example has an estimated weigh of perhaps 1-2 kg but it is rather bulky, still I could carry it with one hand so I would set an encumbrance of 1 to my desklamp. A little bit higher than its actual weight would give it due to its bulkiness. If weight in kg would have been used instead, the desklamp would have a weight of 1,6 kg but that doesn't say anything about its bulkiness, that is something that I have to take into consideration some other way.
To carry wounded comrades (or dog) in a combat situation is covered in the combat section. To carry someone over a longer time, like a shift (5-10 hours), then you have to come up with a solution, like fixing up some kind of stretcher. The actual weight of the person is not important in that case, it is to much for you to be carrying it around in your backpack. A deer is assumed to be worth 2d6 food rations. That is 7 on the average, or 3½ encumbrance. Grenades have weight in the weapon tables (1/4 each for a frag grenade).