It would make sense for soldiers to leave their extraneous equipment back at base camp, but only for something like a planned patrol or a dug in defense. In most of the other situations I can think of, it'd be more likely or make more sense for the soldiers to be carrying everything with them.
In any sort of unexpected attack, the defenders aren't going to take the time to take off all their stuff and put it down, they are going to run into cover and hopefully start repelling the attack.
Attackers are going to want to have their stuff with them too. If they succeed in taking whatever it is they are trying to capture, they are going to want to be able to defend it as well. While a kettle and rations etc don't make the best defensive weapons, a soldier who is fed is more able to fight than one who is hungry. Otherwise the victorious attackers would either have to wait for resupply or they would have to eventually run back to their home base to gather their things. Not a very efficient use of soldiers' time if you have them always running back to base instead of staying put and holding their position.
Only for a patrol of a dug-in defense could a soldier reasonably expect to be able to come back and gather his things.
Now think about the Battle of Stalingrad. There was an awful lot of house to house fighting, with some buildings changing hands multiple times a day. The soldiers fighting there would quickly learn (if they survived more than a day) that the opportunity to advance or the need to retreat might come at any moment, so they would want to be ready to move "camp" at a moment's notice.
The idea of giving a soldier all this gear is to allow him to be somewhat self-sufficient, in case he is cut off from resupply for an extended period of time. If the armies didn't think their soldiers didn't need to have something on themselves at all times they wouldn't have issued it to them.
Now maybe I'm completely wrong and Alan will come in here and tell me I'm an idiot, but it makes a lot of sense to me.
