one of our most imported decision in commercial aviation is about fuel to be loaded.
How is it handled in military aviation? E.g: Do fighters always top off? How is it handled on carriers? Etc,
Tactical military aviation is very different than commercial airliner aviation with regards to fuel loads, and the takeoff fuel loads depend on many factors. However, in general as much fuel would be loaded as the situation permitted. (in other words, you loaded fuel to fill all your tanks, or you loaded fuel till you hit some operational constraint, like max take off weight, max catapult weight, sea state, etc.)
However, military transport and patrol aviation is more similar to commercial aviation. You compute the amount you need for the mission, plus reserves, and load that. In the US P-3 community we computed the amount needed for the mission, plus reserves, and then added 6 klbs "for the wife and kids".
The SR-71 never took off with max fuel. They ALWAYS took off with a light fuel load and then hit a tanker to top off. They essentially never went anywhere without tanker support.
The B-52 has a higher max inflight gross weight than max takeoff gross weight. So when taking off with a big payload requiring long range, they would load enough fuel to reach or nearly reach max takeoff weight and then hit a tanker to add sufficient fuel to reach their max inflight gross weight.