Most "survival rations" are designed according to SOLAS / US Coast Guard requirements that stipulate 2400 KCal per person. Some lifeboats built and equipped to older specifications require 3600 KCal rations to replace their original older style rations. That's why these rations are most commonly found in these sizes. The daily ration is based on the assumption that you are not going to be doing much sitting in a crowded life raft. So, a few hundred calories a day will suffice to keep you alive and functional for a short duration survival circumstance.

Humanitarian rations are similar, often just repackaged survival rations, but again assume a very sedentary existence under refugee camp or similar circumstances. Moreover, they assume the refugees in third world countries for which they are designed are used to existing on substantially less than we are used to eating on a daily basis.

Any other use of these rations is beyond their design scope and must be assessed according to your expected requirements. They are not MREs or field rations of any sort and are not in any way designed to do anything but provide subsistence levels of food for an extended duration.