I don't know why you should not be allowed to take chocolate through security, it's not a liquid. Also, I'd buy the toblerone downstairs on the G level in MUC before going through secondary screening on H level before your US flight. There are just more shops downstairs, I didn't like the few possibilities upstairs.

Usually, there is enough overhead space on LH flights, it never was a problem for me on longhoul.

Sorry, I can't on the ARN shopping possibilities. The overhead space on intra european flights is somewhat limited, so I'd buy it in MUC.