Chocolate and Soreen are both good calls. I use them both. Chocolate is also a mood enhancer. I started using it after meeting a walker at a camp site who was touring Germany and he carried a block of it as his bonk ration for it's calories and it's cheer-up factor.
Marzipan is very energy dense. Chocolate scores high too. Malt loaf is about 1000 cals per bar