when I was in the army I carried sardines, the odd piece of fruit and had all my clothes, not in the army supplied waterproof bag but in a trash bag and individual clothing in eithe trash bags or large ziplock bags, I also carried a book/magazine or two.
If I was going to just go out for guard duty or some other type of b.s Id carry a pair of 45lb weights My ruck would be so heavy Id have to put it on sitting, strap it down and then roll over to my side do a push up and then stand.
Some guys will bring gameboys, or hand held fishing or card games, some smart soldiers bring whole rolls of bunji cords or parachute riggers cord and make themselves hammocks,fishing nets dirty laundry holders, It totally depends, my unit prided itself on if your prepared to hump it you can keep it.
The smartest thing I ever saw anyone carry was a little german army oven the whole thing colapsed down to pocket sized and had these little fuel tablets, the guy actualy Cooked a MRE and a grilled/fried? a potato on it! , he would boil water in the morning so he could have a cup of cofee and have enough left over for shaving, when it cooled a bit he threw it in his pocket for a hand warmer.