She could use her intelligence to outwit Voldemort. Maybe find a loophole in the security around her and make her escape.
Hermione might also get help from unexpected allies. There could be some Death Eaters who are having second thoughts about Voldemort's regime. Or perhaps some magical creatures that she has befriended in the past could come to her rescue.
If she still has her wand, she could perform some powerful and unexpected spells. For example, a spell to create a diversion and then make her getaway while Voldemort and his Death Eaters are distracted.
Percy might try to find Voldemort's Horcruxes and destroy them. This would weaken Voldemort and give Percy a better chance to escape. He could also use his demigod speed and agility to outrun Voldemort's spells and find a way out of the dark wizard's lair.
One way could be through alliances. In the Capitol, there might be some people who secretly support her cause or who are simply against the cruel treatment of captives. She could form an alliance with them and plan an escape. For example, a Capitol servant who has access to keys or security codes could help her. Also, Katniss could pretend to be compliant at first, lulling her captors into a false sense of security before making her move.
Harry might use his wits and the environment around him while in captivity. For example, if he's held in a place with magical artifacts, he could use them to his advantage. He could break the chains that bind him with a spell - enhanced object and then make his way to Voldemort and defeat him.
She could use her intelligence. Maybe she could pretend to cooperate while actually looking for loopholes in their plans or trying to send hidden signals to her friends. For example, she could subtly mislead them about the location of important items or people.
Voldemort may also try to extract information from her. Given Hermione's vast knowledge, he might think she knows secrets about the Order of Phoenix or Dumbledore's plans. He could use various dark magic methods to force her to talk.
Naruto could use his shadow clones to create distractions. He could make a large number of clones and while the Akatsuki members are dealing with the clones, he could find an opening to escape. Also, he might be able to tap into the power of the Nine - Tails more than ever before in a desperate situation, using its strength to break free from any restraints.
Well, if Harry is captured by Voldemort in fanfiction, it could lead to some really dark and intense scenarios. Voldemort might torture Harry to get information about the resistance. Harry, on the other hand, could be secretly planning an escape while pretending to be broken. There could also be a rescue mission by his friends, which would be full of danger and drama.
She might use her intelligence and magic skills. For example, she could create a distraction using a spell like 'Confundo' on her captors and then make a run for it. Hermione is known for her quick thinking, so she could also find a loophole in the security measures set by the Order.
Well, first of all, Percy is a very resourceful character. If he was captured by SHIELD, he'd quickly assess his surroundings. Since he has control over water, he could start by causing a water - related malfunction. For example, if there were any water - cooled systems in the SHIELD facility, he could make them burst. This would create chaos and give him an opportunity to slip away. He could also use his powers to sense any water sources around, like underground water channels. He could then use these as a means of escape, perhaps creating a tunnel of water to swim through. And don't forget his sword, Riptide. He could use it to cut through any barriers or fend off agents if necessary.
He could use his Invisibility Cloak. The Avengers might not be able to detect it with their technology. Then he could find a way to apparate out if he's far enough from any anti - apparition charms.