Gaiters help to keep heather, mud and snow out of your boots and are essential in winter. In winter mittens are better than gloves because you can move your fingers inside them though they are more awkward. Ski goggles also can be useful. In summer sun hat, sunscreen and sunglasses are advisable. To power yourself up hills requires lots and lots of energy.
Fluids are also very important to remain hydrated.
It is a good idea to carry at least a litre of water or juice though this is quite heavy. Hot drinks can be very morale boosting in winter. Carrying some emergency food e.g. some chocolate is advisable. It's pretty essential to carry a whistle and a survival bag - bright, orange plastic bag to shelter in during an emergency. It is also a good idea to carry at least a simple first aid kit.