1. The junk shop is not a "junk shop" per se-it's really an antique store where people could buy things from the time before the war. It is significant because it is here where Winston is reminded of a time before Big Brother and it is here where he gets discovered and captured.
2. The thought police are those that deal with thought crime and any thought contra to Big Brother's hegemony.
3. Vaporizing is significant because this is people are eliminated from existence in Oceania. They become as air, they're vaporized.
4. The significance of the junior anti-sex league is that BB is now using the children as guardians and protectors of the state too. Children will look for thought crime and won't hesitate to turn their parents in for any subordination.
5. The chestnut cafe is significant because that is where Winston ends up, drinking victory alcohol and musing at how he "loves" big brother.